                               In the

    United States Court of Appeals
                For the Seventh Circuit
                    ____________________
Nos. 19‐2090 & 19‐2101
UNITED STATES OF AMERICA,
                                                   Plaintiff‐Appellee,
                                 v.

JONATHAN EYMANN and GARY LYONS,
                                             Defendants‐Appellants.
                    ____________________

        Appeals from the United States District Court for the
                     Central District of Illinois.
          No. 3:15‐cr‐30021 — Sue E. Myerscough, Judge.
                    ____________________

     ARGUED JANUARY 22, 2020 — DECIDED JUNE 12, 2020
                ____________________

    Before WOOD, Chief Judge, and SYKES and HAMILTON, Cir‐
cuit Judges.
    WOOD, Chief Judge. Jonathan Eymann and his uncle, Gary
Lyons, were flying from California to Pennsylvania when they
stopped around midnight at a small public airport in Litch‐
field, Illinois. Suspecting drug traﬃcking, law enforcement
oﬃcers followed the pair to a nearby hotel and confronted
them in the hotel’s parking lot. The encounter ended in their
2                                       Nos. 19‐2090 & 19‐2101

arrests and the discovery of 65 pounds of marijuana in their
airplane.
    Asserting that the oﬃcers had violated the Fourth and
Fifth Amendments in a number of ways, Eymann and Lyons
filed a joint motion to suppress the evidence against them. Af‐
ter the district court denied the motion, Eymann conditionally
pleaded guilty to conspiracy to distribute marijuana, reserv‐
ing the right to appeal the district court’s ruling on their sup‐
pression motion. Lyons proceeded to trial, where a jury con‐
victed him of conspiracy to distribute marijuana and aiding
and abetting the possession of marijuana with the intent to
distribute. Both men now appeal the district court’s denial of
their motion to suppress. Finding no reason to set aside either
the district court’s factual findings or its ultimate conclusion,
we aﬃrm.
                                I
    On July 20, 2013, Department of Homeland Security
(“DHS”) Special Agent Glen Harrington received a call and
an email from Agent Jeﬀ Spencer of DHS’s Air and Marine
Operations Center (“AMOC”) about an airplane that would
be landing that night at the Litchfield Municipal Airport.
Spencer identified the plane as a single‐engine Cessna owned
by Elaine Pate and noted that the pilot would be Pate’s hus‐
band, Lyons. AMOC had been monitoring the Cessna for
months. Although it knew nothing inculpatory about the spe‐
cific plane, owner, and pilot, AMOC found the airplane’s
movement patterns and quick‐turn trips suspicious.
   Spencer’s email, which included information collected by
AMOC research specialist Robert Keller, identified the air‐
plane by its tail number. The email also indicated that on the
Nos. 19‐2090 & 19‐2101                                          3

weekend of May 24, 2013, an unknown pilot flew the airplane
from California to Pennsylvania. The plane stayed in Pennsyl‐
vania for only about fifteen hours before returning to Califor‐
nia. Then, on the weekend of June 21, 2013, it again flew from
California to Pennsylvania and back; this time it remained in
Pennsylvania for only five hours. AMOC identified Lyons as
the pilot during the second trip.
    The email noted additional circumstances that Keller
found suspicious. In January 2013, the Cessna flew to Wat‐
sonville and Cloverdale, California, towns close to a known
marijuana smuggling hub. During the May and June 2013
trips, the plane had landed at small, rural airports late at night
to refuel when the airports were otherwise closed. Keller also
found it odd that the plane apparently had flown through a
serious storm during one of its cross‐country trips. Finally, he
reported that Lyons had been in some economic trouble and
had just emerged from bankruptcy in 2012.
    After evaluating AMOC’s information, Harrington con‐
cluded that the pilot might be using the plane to smuggle
drugs. This was consistent with his experience: every time in
the past when Harrington had pursued a lead based on infor‐
mation provided by AMOC, it led to the seizure of illicit
drugs. Harrington relayed Spencer’s tip to his supervisor,
Resident Agent‐in‐Charge Michael Mitchell. Harrington then
called Lieutenant Lee Jarman of the Litchfield Police Depart‐
ment to coordinate assistance. Harrington and Jarman ar‐
ranged to have a trained drug‐detection dog available for use
that night. They believed that the Cessna would land, refuel,
and take oﬀ again, and Harrington wanted to get a sniﬀ of the
plane while it was on the ground. Jarman contacted the
4                                      Nos. 19‐2090 & 19‐2101

department’s dog handler, Oﬃcer Shane Grammer, and in‐
structed him to be available.
    Harrington arrived in Litchfield at around 11:00 p.m. to
meet with his team at the police department. After a short
briefing, five of them (Mitchell, Harrington, Jarman, former
Chief B.J. Wilkinson, and Oﬃcer Thomas Melchert) headed to
the airport. The oﬃcers watched the area for about an hour;
during which no airplane landed, there were no vehicles en‐
tering or leaving the airport, and the lights were oﬀ inside the
airport’s main building.
     Lyons landed the Cessna at around 12:05 a.m. on July 21,
2013. It taxied behind the airport’s main building and then
parked in an open area. It did not enter a hangar and was not
tethered to the ground. Harrington watched as Eymann and
Lyons removed cargo from the airplane and entered the
building. After a few minutes, the pair left the building and
loaded cargo into the airport’s courtesy car. (Harrington tes‐
tified that he thought their cargo included a box, which he
found suspicious, but no box was found in the later search.
We thus disregard the alleged box.) The courtesy car operates
on an honor system. Users simply provide a driver’s license
number and a signature on a form next to the car keys in the
airport building’s lobby. Lyons signed out the keys, and the
duo left the airport in the courtesy car at around 12:27 a.m.
    As the two men drove oﬀ, Harrington was concerned that
they could be delivering contraband. He saw that possibility
as a “more immediate threat” than the parked airplane at the
airport. The oﬃcers therefore decided to follow the courtesy
car. After a short drive, they saw it pull into a Quality Inn
parking lot. Lyons, who was driving, parked in the last
Nos. 19‐2090 & 19‐2101                                        5

available space. The two then got out of the car and began
walking to the hotel; as they did so, they noticed the oﬃcers.
    Mitchell pulled into the lot as Lyons and Eymann were
parking. He positioned his truck behind the courtesy car, and
Harrington parked nearby. Wilkinson placed his vehicle in
front of the courtesy car, thereby eﬀectively blocking the cour‐
tesy car from moving in any direction. At 12:32 a.m. Mitchell
activated his lights and got out of his truck.
   Mitchell walked over to Lyons, showed his credentials,
identified himself as a law enforcement oﬃcer, and asked to
speak with him. Lyons cooperated while Mitchell asked him
basic questions such as where he was traveling to and from
and the nature of his trip. Lyons replied that he was flying
from California to Pennsylvania for work. The exchange was
conversational, and Mitchell did not raise his voice.
     While Mitchell was speaking with Lyons, Harrington ap‐
proached and asked for Lyons’s identification. After receiving
it, he approached Eymann with the same request. Harrington
took both identification cards back to his vehicle to check for
outstanding warrants.
    Meanwhile, as Mitchell continued to speak with Lyons,
Lyons suddenly became flush and fainted, collapsing into
Mitchell. The oﬃcers placed him in the front passenger seat
of Wilkinson’s vehicle with the door open and the air condi‐
tioning on. They did not question him any further at that
point about anything other than his medical condition.
   While others saw to Lyons, Harrington discovered that
neither man had an active warrant. Harrington then ap‐
proached Eymann and asked him some questions about Ly‐
ons’s health. He also asked Eymann if he had brought any
6                                      Nos. 19‐2090 & 19‐2101

marijuana from California. Eymann admitted that he had a
small, personal‐use, amount of marijuana in the car.
    Eymann’s admission prompted an escalation in the en‐
counter. Jarman ordered Grammer and his drug‐dog Arie to
the scene at 12:33 a.m.; they arrived around 12:54 a.m. Gram‐
mer and Arie got to work right away, and shortly thereafter
Arie positively alerted at the front passenger door seam.
Grammer rewarded Arie with a towel to chew on, while the
oﬃcers opened the car, removed the items, and spaced them
out on the ground. (There was some dispute in the district
court about the sequence of events: did Arie’s alert come first
and then the search of the car, or vice versa? Eymann and Ly‐
ons have not pursued this on appeal, and so we do not need
to resolve the point.) Arie alerted on a piece of luggage, which
the oﬃcers then searched. Once again, Arie was rewarded.
The oﬃcers found a small amount of marijuana (about 2.5
grams) within the luggage.
    Around the time Arie was sniﬃng around the courtesy
car, Harrington frisked Lyons. During the frisk, Harrington
felt what he thought was a stack of money in Lyons’s front
cargo pocket. Harrington asked Lyons what was in his pocket,
and Lyons replied that he had $1,600 in an envelope for fuel
and expenses; the envelope actually contained $2,600. Arie
later sniﬀed the envelope and alerted.
    After the oﬃcers found the marijuana, they handcuﬀed
and arrested both Eymann and Lyons. They then transported
the pair back to the airport, which they entered through the
airport gate with the permission and assistance of airport
agents. The Cessna was still the only airplane on the tarmac,
and the airport still looked empty.
Nos. 19‐2090 & 19‐2101                                         7

    Grammer walked Arie around the Cessna for another
sniﬀ, and Arie provided another positive alert, followed as be‐
fore by a reward. The oﬃcers opened the plane using a key
they had seized from Lyons, and they immediately smelled
marijuana. This time the quantity was considerable. The oﬃc‐
ers placed several bags from inside the plane on the tarmac
and had Arie check each one. He alerted on three of them and
(following a now‐familiar pattern) received a reward. The of‐
ficers searched the bags and found a total of 65 pounds
(roughly 29.5 kilograms) of marijuana. In a later search of the
airplane, they also found a firearm.
    In July 2013, the Montgomery County State’s Attorney
charged Eymann and Lyons with possession of over 500
grams of marijuana. They filed a motion to suppress evidence,
arguing that Arie was not properly certified through the State
of Illinois at the time of the sniﬀs. Although Arie had com‐
pleted the necessary training to be certified by the state, his
certification had lapsed weeks before as a result of an admin‐
istrative error. After a hearing, the state court determined
that, because of Arie’s lapse in certification, Arie’s alerts did
not provide probable cause. It granted the defendants’ mo‐
tion, and the state later dismissed the charges.
    That proved to be just the end of the beginning, not the
beginning of the end, of Eymann and Lyons’s troubles. On
May 6, 2015, a federal grand jury returned an indictment
charging both of them with conspiracy to distribute mariju‐
ana, in violation of 21 U.S.C. §§ 846, 841(a)(1) and (b)(1)(D),
and aiding and abetting the possession of marijuana with the
intent to distribute, in violation of 21 U.S.C. §§ 841(a)(1),
(b)(1)(D), and 18 U.S.C. § 2. Lyons was also charged with
8                                      Nos. 19‐2090 & 19‐2101

carrying a firearm during and in relation to a drug traﬃcking
crime, in violation of 18 U.S.C. § 924(c)(1)(A)(i).
    In October 2015, Lyons and Eymann filed a joint motion to
suppress evidence and a supporting memorandum; they al‐
leged multiple constitutional violations during their encoun‐
ter with law enforcement. The district court held a hearing on
the motion and, in October 2016, denied it. Two years later,
Eymann entered a conditional plea of guilty to conspiracy to
distribute marijuana, reserving the right to appeal the district
court’s suppression decision. Lyons proceeded to trial, and a
jury convicted him of conspiracy to distribute marijuana and
aiding and abetting the possession of marijuana with the in‐
tent to distribute; it acquitted him of the gun charge. The dis‐
trict court sentenced Eymann to 10 months’ imprisonment
and Lyons to concurrent sentences of 27 months on each
count.
                               II
    We review a district court’s denial of a motion to suppress
under a dual standard of review: we apply the clear error
standard to its factual determinations, with special deference
to its credibility determinations, United States v. Villalpando,
588 F.3d 1124, 1127 (7th Cir. 2009); but we take a de novo ap‐
proach to its conclusions of law. Id.
                               A
    Eymann and Lyons first contend that all the evidence the
police collected must be suppressed because it all flowed from
the encounter in the Quality Inn parking lot, and that encoun‐
ter was, at a minimum, an impermissible Terry stop that was
not supported by reasonable suspicion. They also argue that
Nos. 19‐2090 & 19‐2101                                        9

even if the oﬃcers had reasonable suspicion to do something,
their actions exceeded the scope of a Terry stop.
    The Fourth Amendment protects persons from “unreason‐
able searches and seizures.” U.S. Const. amend. IV. Generally,
seizures are “reasonable” only when they are based on prob‐
able cause. Dunaway v. New York, 442 U.S. 200, 213 (1979). The
Supreme Court recognized an exception to the probable‐
cause rule in Terry v. Ohio, 392 U.S. 1 (1968). Under Terry, po‐
lice oﬃcers may briefly detain a person for investigatory pur‐
poses based on the less exacting standard of reasonable sus‐
picion that criminal activity is afoot. 392 U.S. at 21–22.
    Terry does not, however, lift all restrictions on police ac‐
tion. Reasonable suspicion exists only when an oﬃcer can
point to “specific and articulable facts which, taken together
with rational inferences from those facts, reasonably warrant
that intrusion.” Id. at 21. In making reasonable‐suspicion de‐
terminations, we “look at the ‘totality of the circumstances’ of
each case to see whether the detaining oﬃcer has a ‘particu‐
larized and objective basis’ for suspecting legal wrongdoing.”
United States v. Arvizu, 534 U.S. 266, 273 (2002). Reasonable
suspicion requires more than an “inchoate and unparticular‐
ized suspicion or ‘hunch’” but “considerably less than pre‐
ponderance of the evidence.” Illinois v. Wardlow, 528 U.S. 119,
123–24 (2000). Ultimately, the determination of reasonable
suspicion “must be based on commonsense judgments and
inferences about human behavior.” Id. at 125.
    Eymann and Lyons argue that the oﬃcers had nothing
more than a hunch when they stopped the two men in the ho‐
tel parking lot, but the record demonstrates otherwise. First,
the oﬃcers on the scene were aware of the suspicious details
of the plane’s and pilot’s flight history. Based on AMOC’s tip,
10                                      Nos. 19‐2090 & 19‐2101

the oﬃcers knew that at least twice, the plane had flown from
California to Pennsylvania and back and remained on the
ground for only a matter of hours before returning. Oﬃcers
also knew that Lyons was the pilot on at least one trip. Such
quick‐turn flights, although not necessarily illegal, may con‐
tribute to reasonable suspicion of criminal conduct. See, e.g.,
United States v. Sokolow, 490 U.S. 1, 9 (1989) (flying 20 hours
from Hawaii to Florida and staying only 48 hours in Florida
contributed to reasonable suspicion); United States v. Simpson,
609 F.3d 1140, 1151–52 (10th Cir. 2010) (driving from Ne‐
braska to spend only one night in Reno contributed to a find‐
ing of reasonable suspicion); United States v. Ehlebracht, 693
F.2d 333, 337 (5th Cir. 1982) (four hour and 30 minute stop
before returning after a long trip was suspicious).
    In addition, during these quick‐turn flights, the plane of‐
ten landed at small, rural airports to refuel at hours when the
airports and airport buildings were eﬀectively closed. Alt‐
hough such travel patterns are not illegal, they may contribute
to reasonable suspicion, given that they could assist in shield‐
ing criminal conduct from detection. United States v. Michel,
588 F.2d 986, 998 (5th Cir. 1979) (finding reasonable suspicion
in part because “small country airports [a]re often used by
marijuana smugglers to fly loads in after the airfields closed”).
This factor may cut both ways, however, because a pilot who
lands at a closed airport apparently must use a credit or debit
card to refuel from a self‐service gas pump. This leaves a pa‐
per trial that could be avoided by refueling at an open airport
where the pilot could pay with cash.
    The district court also noted that the agents were aware
that the plane had flown to Watsonville and Cloverdale, Cal‐
ifornia—places where AMOC had previously found drug
Nos. 19‐2090 & 19‐2101                                           11

traﬃcking. Courts have held that flights to or from high drug
traﬃcking areas may properly contribute to reasonable suspi‐
cion. See United States v. Espinosa‐Alvarez, 839 F.2d 1201, 1206
(7th Cir. 1987); United States v. Palen, 793 F.2d 853, 857 (7th Cir.
1986). On the other hand, in this era of increasing legalization
of marijuana, coupled with widespread cultivation, we con‐
sider this only a small nudge in the direction of reasonable
suspicion.
    We do agree with the district court’s determination that
the airplane’s alleged travel through bad weather did not con‐
tribute to reasonable suspicion. In his email, Keller flagged
that the plane had flown through a storm. The radar image
that AMOC provided, however, did not show the plane flying
through bad weather. Instead, it showed the plane’s flight
path over Indiana and Illinois. Stormy weather is visible in the
plane’s past route at the time the image was captured. That
picture is not evidence that the stormy weather existed when
the plane was in that spot; the storm clouds could have moved
into the route after the plane had flown by.
    Eymann and Lyons attack the evidence we have just sum‐
marized with the contention that the agents should not have
relied on any information provided by Keller. They argue that
this basis is no better than the one in Florida v. J.L., 529 U.S.
266 (2000), where the Supreme Court found that police lacked
reasonable suspicion for a Terry stop. Id. at 274. There, the of‐
ficers’ suspicion that the defendant was carrying a weapon
“arose not from any observations of their own but solely from
a call made from an unknown location by an unknown
caller.” Id. at 270. Also, the anonymous call concerning the de‐
fendant “provided no predictive information and therefore
left the police without means to test the informant’s
12                                      Nos. 19‐2090 & 19‐2101

knowledge or credibility.” Id. at 271. Eymann and Lyons em‐
phasize that Harrington had never dealt with Keller and thus
could not assess Keller’s reputation. In addition, they say,
whereas the J.L. defendant’s carrying of a firearm was a crime,
no one reported any crime by them. Keller reported only sus‐
picions about otherwise lawful activity.
    But Keller and Spencer were far from anonymous inform‐
ants. They both worked for DHS’s Air and Marine Operations
Center, which is part of DHS’s Customs and Border Protec‐
tion section and which, according to its website, “uses sophis‐
ticated technology to detect, identify, track, and direct the in‐
terdiction of suspect aviation and maritime targets in the
Western Hemisphere.” See cbp.gov, Air and Marine Opera‐
tions Leadership and Organization. One of AMOC’s jobs is to
monitor airplane activity to reduce drug traﬃcking by air.
Spencer and Keller were both acting within the scope of their
oﬃcial responsibilities when they passed along their infor‐
mation about the Cessna to Harrington. Also, a similar tip
from AMOC in the past had led to the seizure of illegal drugs.
Spencer gave Harrington specific details, and the Litchfield
team witnessed firsthand activity by Eymann and Lyons that
corroborated the tip. Finally, the possible lawfulness of a per‐
son’s actions does not defeat reasonable suspicion. See
Navarette v. California, 572 U.S. 393, 403 (2014).
    The information that Harrington received from Keller (via
Spencer) also falls within the collective‐knowledge doctrine.
Under the collective‐knowledge doctrine, oﬃcers may carry
out a stop even if they do not have firsthand knowledge of the
facts amounting to reasonable suspicion. See United States v.
Harris, 585 F.3d 394, 400 (7th Cir. 2009). Instead, “where law
enforcement authorities are cooperating in an investigation,
Nos. 19‐2090 & 19‐2101                                        13

as here, the knowledge of one is presumed shared by all.” Il‐
linois v. Andreas, 463 U.S. 765, 771 n.5 (1983). Collective
knowledge also applies to information that an oﬃcer receives
from those with the “training, responsibility or authority to
make a determination of reasonable suspicion.” United States
v. Colon, 250 F.3d 130, 137 (2d Cir. 2001).
    Spencer was a law‐enforcement oﬃcer at AMOC. Harring‐
ton and the other DHS and LPD oﬃcers involved in the stop
were entitled to rely on Spencer’s information, including the
report he received from Keller. Keller, as an intelligence re‐
search specialist at AMOC, is responsible for detecting suspi‐
cious activity among airplanes and sharing that information
with the appropriate oﬃcer(s). Therefore, the information
Harrington received from Spencer, which included infor‐
mation from Keller, properly contributed to a finding that the
oﬃcers had reasonable suspicion to stop Eymann and Lyons
in the hotel parking lot.
                               B
    The next question is whether the parking‐lot encounter ex‐
ceeded the scope of a Terry stop. To be lawful, “a detention
must be limited in scope and executed through the least re‐
strictive means.” United States v. Ienco, 182 F.3d 517, 523 (7th
Cir. 1999). “A seizure becomes an arrest when a reasonable
person in the suspect’s position would have understood the
situation to constitute a restraint on freedom of movement of
the degree which the law associates with formal arrest.” Id.
(internal quotation marks omitted). “The line between a law‐
ful Terry stop and an unlawful arrest is not bright.” United
States v. Askew, 403 F.3d 496, 507 (7th Cir. 2005). “Several fac‐
tors are relevant in deciding whether a Terry stop has become
an arrest[,] including the oﬃcer’s intent in stopping the
14                                     Nos. 19‐2090 & 19‐2101

individual, whether there was a search, whether, or how
much, questioning occurred, whether there was a show of
force and whether the person stopped could be said to have
been taken into custody.” United States v. Rodriguez, 831 F.2d
162, 166 (7th Cir. 1987).
    Eymann and Lyons, with the support of our dissenting
colleague, argue that the encounter in the parking lot, before
they were handcuﬀed, was more akin to an arrest than the
limited detention permitted under Terry. They point to the fol‐
lowing factors: the encounter occurred at night; the agents did
not advise them that they were free to leave; the agents
parked their vehicles in a way that did not allow the courtesy
car to leave; two of the police vehicles activated emergency
lights; the agents stood close to the two men and blocked their
entrance to the hotel; several oﬃcers were present and their
weapons were visible; and the oﬃcers took the men’s identi‐
fication cards.
    The answer to the question whether they were under ar‐
rest depends significantly on the underlying facts. The district
court found that there was no arrest until the oﬃcers hand‐
cuﬀed the two after they found marijuana in Eymann’s bag.
The earlier show of force, it found, was minimal. Although
there were quite a few uniformed oﬃcers and police cars, and
some of the cars had flashing lights, the oﬃcers did not draw
any weapons or raise their voices. This level of force is nor‐
mally not associated with a formal arrest. See Askew, 403 F.3d
at 508−09 (surrounding suspect’s car to prevent him from
leaving did not convert stop into arrest). In addition, the of‐
ficers investigated their suspicions by questioning Eymann
and Lyons immediately. These actions aligned with the pur‐
pose of the investigatory stop, as oﬃcers are “permitted to ask
Nos. 19‐2090 & 19‐2101                                         15

questions to determine an individual’s identity and to obtain
information confirming an oﬃcer’s suspicions.” United States
v. Johnson, 680 F.3d 966, 974 (7th Cir. 2012), overruled on other
grounds by Fowler v. Butts, 829 F.3d 788 (7th Cir. 2016); see
Hiibel v. Sixth Judicial Dist. Court of Nevada, Humboldt Cnty, 542
U.S. 177, 187–88 (2004). The duration of the questioning was
also brief. The oﬃcers asked the pair about their travel plans
until Lyons experienced his medical episode. At that point,
the oﬃcers turned their focus to Eymann. Agent Harrington
asked Eymann whether he had brought any marijuana. The
tone, the district court found, was calm and conversational,
and the questioning did not indicate that either Eymann or
Lyons was under arrest at that point.
    Eymann and Lyons’s strongest argument is that the oﬃc‐
ers themselves characterized the stop as an arrest at the state
suppression hearing. Worse, they say, Wilkinson’s and Jar‐
man’s testimony at the state suppression hearing in March
2014 actually conflicted with their testimony at the federal
suppression hearing in 2015 and 2016. Eymann and Lyons
emphasize that, at the state‐court suppression hearing, Wil‐
kinson unequivocally said that the defendants were “in cus‐
tody” when the police oﬃcers arrived at the Quality Inn park‐
ing lot, and his choice of that phrase amounts to an admission
that the stop was an arrest. At that point, they contend, the
oﬃcers lacked probable cause to make those arrests, and so
the arrests were illegal and the evidence gathered afterwards
must be suppressed.
   We have taken a close look at both the state‐court and the
federal‐court records, however, and we are satisfied that they
are not in conflict. At both hearings, Wilkinson and Jarman
emphasized that Eymann and Lyons were “not free to leave”
16                                      Nos. 19‐2090 & 19‐2101

from the moment the oﬃcers arrived at the Quality Inn park‐
ing lot. In addition, at both hearings, Wilkinson equated “not
free to leave” with being in custody. Wilkinson’s use of the
word “custody” (which he uses at both hearings) appears to
be based on the fact that the defendants were not free to leave.
There is no reason to think that he was oﬀering a legal opinion
about whether their situation qualified as “custody” under
the law. See Thompson v. Keohane, 516 U.S. 99, 112–13 (1995)
(ultimate question whether a person is “in custody” is a
mixed question of law and fact and receives plenary review).
    We learn little from the fact that the defendants were not
free to leave, because that is also true in standard Terry stops.
That constraint signals only that the interaction was not
merely a consensual encounter. See United States v. Williams,
945 F.2d 192, 196 (7th Cir. 1991). Moreover, the question
whether a person is under arrest is an objective one, not one
that depends on the oﬃcers’ beliefs. Ienco, 182 F.3d at 523.
   Because the oﬃcers used little show‐of‐force, kept their
questioning within reasonable bounds, and acted consistently
with an investigatory detention, we conclude, as the district
court did, that a reasonable person would not have under‐
stood that his freedom was restrained to the degree associated
with a formal arrest during the period before the handcuﬃng.
                               C
    Eymann and Lyons next argue that the oﬃcers did not
have probable cause to search the car. Probable cause to
search a vehicle exists “if, given the totality of the circum‐
stances, there is a fair probability that contraband or evidence
of a crime will be found in a particular place.” United States v.
Scott, 516 F.3d 587, 589 (7th Cir. 2008) (internal quotation
Nos. 19‐2090 & 19‐2101                                         17

marks omitted). “Admissions of crime, like admissions
against proprietary interests, carry their own indicia of credi‐
bility—suﬃcient at least to support a finding of probable
cause to search.” United States v. Harris, 403 U.S. 573, 583
(1971). Once Eymann admitted to having marijuana in the car,
the oﬃcers had probable cause to search it, unless there is
some problem with the admission.
    That is the route Eymann tries to take. He says that he was
under arrest before he made the admission and that he made
the statement only in response to Agent Harrington’s post‐ar‐
rest questioning. That taints the admission, he argues, be‐
cause he had not yet received his Miranda warnings, and so it
cannot be used to establish probable cause. One problem with
this argument is that, as the district court found, Eymann had
no privacy interest in the car and thus could not challenge its
search. We need not opine on that point. Eymann’s argument
works only if he was in custody while he was being ques‐
tioned, and we have concluded that he was not. His admission
therefore gave the oﬃcers probable cause to search the cour‐
tesy car.
                                D
   Once the marijuana was found in Eymann’s luggage, the
oﬃcers had probable cause to arrest Eymann. We are left with
Lyons’s arguments about his frisk and arrest.
    We start with the frisk. “For a frisk to be lawful, it must be
based on reasonable suspicion that ‘criminal activity may be
afoot and that the persons with whom [the oﬃcer] is dealing
may be armed and presently dangerous.’” United States v.
Lopez, 907 F.3d 472, 485 (7th Cir. 2018) (quoting Terry, 392 U.S.
at 30). “[G]iven the … burdensome intrusion of a frisk, such
18                                          Nos. 19‐2090 & 19‐2101

action should only be allowed when the oﬃcer can point to
articulable facts that would establish the separate and specific
condition that the detainee has a weapon or poses some dan‐
ger.” United States v. Williams, 731 F.3d 678, 686 (7th Cir. 2013).
    Lyons asserts that the oﬃcers had no reason to think he
was armed or dangerous. He emphasizes that mere suspicion
of drug traﬃcking is insuﬃcient to justify a frisk. Lyons, how‐
ever, failed to raise this argument before the district court, and
so he may not raise it now for the first time on appeal. Puﬀer
v. Allstate Ins. Co., 675 F.3d 709, 718 (7th Cir. 2012). Although
the motion to suppress contained many arguments, an im‐
proper frisk was not one of them.
                                  E1
    We now turn to Lyons’s arrest. Lyons argues that the of‐
ficers did not have probable cause to arrest him after they
found Eymann’s marijuana. “Probable cause for an arrest ex‐
ists if an oﬃcer reasonably believes, in light of the facts and
circumstances within his knowledge at the time of the arrest,
that the suspect has committed, or is committing, an oﬀense.”
Thompson v. Wagner, 319 F.3d 931, 934 (7th Cir. 2003), as
amended on denial of reh’g (Mar. 14, 2003). We must “exam‐
ine the events leading up to the arrest” and then determine
“whether these historical facts, viewed from the standpoint of
an objectively reasonable police oﬃcer, amount to” probable
cause. Maryland v. Pringle, 540 U.S. 366, 371 (2003).



     1
     Section II.E. represents the views of only Chief Judge Wood. As ex‐
plained in her concurrence, Judge Sykes concludes that the officers had
probable cause to arrest Lyons. Judge Hamilton dissents on grounds ex‐
plained in his separate opinion.
Nos. 19‐2090 & 19‐2101                                        19

    The district court found that there was probable cause to
arrest Lyons because the oﬃcers knew that (1) he had been in
the car with both Eymann and Eymann’s marijuana, (2) he
had been carrying $2,600 in cash (and missed by a thousand
dollars how much he had, when he responded to the oﬃcer’s
question), (3) he unloaded a box from a plane that had been
involved in numerous quick‐turn trips and that often landed
at rural, closed airports, and (4) upon being confronted by law
enforcement, he experienced a fainting episode. The district
court also cited Pringle, 540 U.S. 366, noting that the Supreme
Court held that oﬃcers who found drugs in a car had proba‐
ble cause to arrest all three of the car’s passengers where the
drugs were accessible to all three men and all three failed to
oﬀer information about the drugs’ ownership.
    Pringle is not very helpful, as it is easily distinguishable.
Whereas the suspects in Pringle refused to concede ownership
of the drugs, Eymann frankly admitted to his ownership of
his personal‐use marijuana. The oﬃcers had no reason to
doubt Eymann’s claim that the drugs were his, and the quan‐
tity did not lend itself to a shared‐ownership theory. The
other reasons the district court listed for finding probable
cause are also weak. Although Lyons experienced a fainting
spell, “[m]ost people, when confronted by a police oﬃcer, are
likely to act nervous, avoid eye contact, and even potentially
shift their bodies as if to move away from the area.” Williams,
731 F.3d at 687. And, as noted earlier, the question whether
there was a box at all is disputed, much less whether the ex‐
istence of a box on an airplane—one that did not make it into
the courtesy car—is anything but innocuous. For these rea‐
sons, Chief Judge Wood concludes that the oﬃcers did not
have probable cause to arrest Lyons.
20                                      Nos. 19‐2090 & 19‐2101

                               F
    Our focus, however, is on the evidence the police seized,
not the validity of the arrest for its own sake. Lyons and Ey‐
mann argue that Lyons’s unlawful arrest led to the search of
the Cessna, and so the evidence of the marijuana stash must
be suppressed. (As nothing turns on it, we assume for present
purposes that both had enough interest in the Cessna to com‐
plain about this search.) They note that when the oﬃcers ar‐
rested Lyons, they found and took the airplane’s keys, and
they used those keys to open the airplane during the search.
The pair compares these events to the events in United States
v. Ienco, 182 F.3d 517 (7th Cir. 1999). In Ienco, police arrested
two men without probable cause. Id. at 524−25. While the two
were unlawfully detained in the back of the police car, one
accidentally dropped the key to their van. Id. at 528. Hours
later, the police found the key and used it to gain access to the
van, where they found weapons. Id. at 522. Aﬃrming the dis‐
trict court’s motion to suppress the weapons as evidence, we
held that “if the arrest was illegal, evidence obtained by the
discovery of the key hidden in the police car and the ensuing
discovery, impoundment, and search of the van would be in‐
admissible, all that being the fruit of the unlawful arrest.” Id.
at 526, 529.
    The government argues that even if the arrest was im‐
proper, the inevitable‐discovery doctrine applies, and on that
basis the evidence from the airplane should not be sup‐
pressed. Under the inevitable‐discovery doctrine, if the pros‐
ecution can establish by a preponderance of the evidence that
the challenged evidence ultimately would have been discov‐
ered through lawful means without regard to the constitu‐
tional error, then the evidence is not subject to suppression.
Nos. 19‐2090 & 19‐2101                                                      21

United States v. Jones, 72 F.3d 1324, 1330 (7th Cir. 1995). To sat‐
isfy this burden the government must demonstrate (1) that “it
had, or would have obtained, an independent, legal justifica‐
tion for conducting a search that would have led to the dis‐
covery of the evidence,” and (2) that it “would have con‐
ducted a lawful search absent the challenged conduct.” United
States v. Marrocco, 578 F.3d 627, 637–38 (7th Cir. 2009). The
doctrine is premised on the idea that law enforcement
“should be placed in no better, but no worse, a position than
they would have been had no impropriety occurred.” Jones,
72 F.3d at 1330.
    Although the district court did not reach inevitable dis‐
covery (because it found no constitutional errors), our conclu‐
sion with respect to Lyons’s arrest makes it necessary for us
to address this point. We may do so, because the parties de‐
veloped the necessary record in the district court.2 The first
question is whether the government had an independent, le‐
gal justification for conducting the search of the plane that led
to the discovery of the marijuana. We are satisfied that it did.
When the oﬃcers returned to the airport after the encounter
in the hotel parking lot, they entered the airport gate with the
permission and assistance of the airport agents. The oﬃcers
were therefore lawfully present on the runway. Moreover, the
oﬃcers were permitted to bring Arie to the plane and instruct
him to conduct an outdoor sniﬀ test. Police oﬃcers need no
articulable reason to call in a drug‐sniﬃng dog as long as do‐
ing so does not otherwise invade a person’s legitimate interest
in privacy. See United States v. Jacobsen, 466 U.S. 109, 123 (1984)

    2 The dissent believes that further development of this issue is needed

in the district court. Post at 12. With respect, we see no critical gaps in the
record that require filling.
22                                      Nos. 19‐2090 & 19‐2101

(“[G]overnmental conduct that can reveal whether a sub‐
stance is cocaine, and no other arguably ‘private’ fact, com‐
promises no legitimate privacy interest.”); United States v.
Place, 462 U.S. 696, 707 (1983) (establishing that a dog’s sniﬀ
of luggage does not constitute a Fourth Amendment search).
Neither Lyons nor Eymann had a legitimate privacy interest
in the marijuana in the plane. Moreover, deploying Arie did
not invade Eymann’s or Lyons’s legitimate privacy interest
because the airplane was parked on an open runway. See
United States v. Grogg, 534 F.3d 807, 810–11 (7th Cir. 2008)
(“[T]he Supreme Court has made clear that a dog sniﬀ in a
public place is not a search[,] because it is unique, in that it
does not intrude on or disclose any information other than
whether contraband is present, and a possessor of contraband
cannot maintain a legitimate expectation that the contra‐
band’s presence will not be revealed.”).
    If Arie’s alert on the airplane survives scrutiny, then it
gave the oﬃcers probable cause to search the plane independ‐
ent of anything that happened at the hotel. Lyons and Ey‐
mann contend that reliance on the dog’s alert was improper,
however, because Arie was uncertified at the time he sniﬀed
the airplane. They also claim Arie was unreliable. The record
establishes otherwise.
   We should first say that the question whether Arie did or
did not have a particular state certificate is a question of state
law. The Fourth Amendment does not incorporate such state
requirements; it asks only whether, objectively, the oﬃcers
had probable cause to search. The record showed that Arie
successfully completed many training sessions. Starting in
2007, Arie completed a 10‐week program at the Illinois State
Police Canine Academy. He was trained to detect various
Nos. 19‐2090 & 19‐2101                                       23

drug odors and to refrain from alerting when odors other than
the specified set (proofing odors) were present. At the end of
the 10‐week program, Arie was tested and evaluated in 32 dif‐
ferent categories, and he received passing marks in each cate‐
gory. After that program, Arie successfully completed a three‐
to five‐day refresher training at the Academy in 2008, 2009,
2010, 2011, and 2012. During each refresher course, Arie was
tested in at least 32 categories and passed in all evaluated ar‐
eas. The most recent refresher course Arie completed before
July 2013 was in November 2012, less than eight months be‐
fore the sniﬀ. He earned a perfect score in 36 evaluated areas.
    Outside of the Academy, Grammer and Arie completed
bi‐weekly trainings with other handler/dog teams. Arie also
participated in additional out‐of‐state training programs. In
addition, during a July 2012 session, Arie received special
recognition for being the only dog successfully to pass a com‐
plex proofing odors test; the training included about 75 dif‐
ferent proofing odors and no drug odors, and Arie was the
only dog that went through the entire building without giving
a single false alert.
    Despite this record, Eymann and Lyons argue that Arie
was not reliable. They assert that Arie receives a reward every
time he alerts, even when no drugs are found, and so he is
motivated to alert during every drug sniﬀ. In fact, the data
from 2012, they argue, shows that Arie performed 29 drug
sniﬀs and alerted positively to the presence of drugs in all of
them. In addition, they contend that even though Arie has
been trained to alert passively, the evidence shows that he
was aggressively alerting during the sniﬀs. These active
alerts, they insist, undermine the district court’s reliability
finding. Eymann and Lyons also emphasize that Arie was not
24                                               Nos. 19‐2090 & 19‐2101

properly certified during the sniﬀs. They note that even a
well‐trained dog is not permitted to search for drugs once its
certification expires.
    Taking the last point first, we reiterate that Arie’s lack of a
state certificate is not conclusive for federal constitutional
purposes. His lack of certification was attributable to an ad‐
ministrative error, not incompetence on the job. Once the er‐
ror was spotted, the state retroactively certified Arie for the
period that included the events in question. Even in the ab‐
sence of formal certification, “evidence of a dog’s satisfactory
performance in a certification or training program can itself
provide suﬃcient reason to trust his alert.” Florida v. Harris,
568 U.S. 237, 246 (2013). In addition, the 2012 data that Ey‐
mann and Lyons claim shows that Arie alerted positively
100% of the time was actually a record of only Arie’s positive
alerts, not of all of the drug sniﬀs he performed. Moreover,
Arie’s handler, Grammer, testified that Arie provided a pas‐
sive alert during the sniﬀs. Although Wilkinson testified that
Arie stopped, sat, and barked at the seam door, which the de‐
fendants argue is not a passive alert, the actions of stopping
and sitting are consistent with a passive alert. In addition,
Grammer was likely paying more attention to Arie’s actions
during the sniﬀs. We therefore agree with the district court
that at the time of his sniﬀ of the plane, Arie’s alert could and
did establish probable cause.3


     3 The dissent queries whether the “automobile exception” to the
Fourth Amendment applies to a small airplane such as the Cessna. The
issue, we believe, is not properly before us, because the defendants did
not raise this point until their reply briefs. The dissent disagrees, asserting
that “the [automobile‐exception] question arose only in reply to the gov‐
ernment’s reliance on inevitable discovery as an alternate ground to
Nos. 19‐2090 & 19‐2101                                                       25

    This brings us to the second inquiry for inevitable discov‐
ery: the government must demonstrate that it would have
conducted a lawful search absent the challenged conduct. Ex‐
cept for Oﬃcer Wilkinson, the oﬃcers and agents are clear in
their testimony that they were going to bring Arie to the plane
to perform a sniﬀ test regardless of what happened at the ho‐
tel. When asked if there was any circumstance where he
would not have called Grammer to walk Arie around the
plane, Jarman replied that he “would have ran [sic] that dog
no matter what [the agents] had decided” because he had pre‐
viously found drugs in a plane at the airport and did not want
the Litchfield Municipal Airport to be a stop for drug couriers.
Harrington testified that there were no circumstances under
which he would not have made use of a drug‐detection dog.
He also testified that even if the Litchfield Police Department
did not make Arie available, he “would have contacted Illi‐
nois State Police and arranged for one of their [dogs] to as‐
sist.” Mitchell testified that “regardless of how following that
car turned out,” “we would have definitely run the [dog]
around the plane.” Wilkinson’s testimony was more equivo‐
cal. He said that if the federal agents decided not to run the

affirm.” Post at 13 n.1. In their opening briefs, however, the defendants
argued that the search of the Cessna was unlawful because Arie’s alert
could not establish probable cause. We would reach the probable‐cause
question only if the automobile exception applied to the Cessna. The de‐
fendants therefore should have taken issue with the district court’s deter‐
mination that the automobile exception applied in their opening briefs.
We note as well that a number of circuits have found that the same ap‐
proach applies to airplanes. See, e.g., United States v. Linn, 30 F.3d 132, 1994
WL 399179, at *2 (4th Cir. 1994) (unpublished); United States v. Rollins, 699
F.2d 530, 534 (11th Cir. 1983); United States v. Gooch, 603 F.2d 122, 124 (10th
Cir. 1979). Because the issue has not been properly presented here, we do
not need to resolve this point.
26                                      Nos. 19‐2090 & 19‐2101

dog around the plane, he was not sure whether he would have
ordered Arie to be deployed. He “would have had to try to
validate why their suspicion was no longer valid or [why]
they didn’t want to pursue their suspicion, and then [he
would] have to make a decision.”
    Wilkinson’s lack of certainty is not enough, in our view, to
overcome the testimony of all the other oﬃcers to the eﬀect
that the airplane was the central focus of their interest. This
record shows that they would have walked Arie around the
plane even if they had not improperly arrested Lyons. Both
Eymann, whose arrest does pass muster, and Lyons were in
the plane, and all the other information suggesting that the
plane was being used for illegal drug operations was still
there. Wilkinson indicated that he would probably have de‐
ferred to the federal agents, and the federal agents testified
that they would have deployed Arie no matter what. Lyons’s
arrest was largely beside the point. The inevitable‐discovery
doctrine therefore applies, and the district court correctly re‐
fused to suppress the evidence found in the plane.
                               G
    Lastly, Lyons argues that the district court erred in finding
that the government was not collaterally estopped from liti‐
gating the suppression hearing in federal court. Recall that be‐
fore the federal charges were filed, the Montgomery County
Circuit Court found that Arie’s alerts on the courtesy car and
the plane could not establish probable cause because Arie was
not technically certified as a drug‐detection dog during those
sniﬀs. The state court determined that 50 ILCS 705/10.12 pre‐
cluded finding probable cause from an alert by an uncertified
dog. That finding prompted the state court to suppress the
evidence from the plane.
Nos. 19‐2090 & 19‐2101                                        27

    Collateral estoppel (or as we now say, issue preclusion) is
“properly applied when an issue raised by a party to a suit
has been actually and necessarily litigated in a prior suit and
when the party against whom estoppel is asserted has had a
‘full and fair opportunity’ to litigate the issue.” United States
v. Sherman, 912 F.2d 907, 909 (7th Cir. 1990). “The four require‐
ments of collateral estoppel are that: (1) the issue sought to be
precluded is the same as that involved in the prior action; (2)
the issue was actually litigated; (3) the determination of the
issue was essential to the final judgment; and (4) the party
against whom estoppel is invoked was fully represented in
the prior action.” Id.
    Requirement 4 is not met here. Lyons argues that the state
suppression hearing provided the federal government a full
and fair opportunity to vindicate its rights, but the United
States was not a party to the state action or otherwise repre‐
sented in it. Issue preclusion “cannot apply here because it
holds only between the same parties, whereas the United
States was not represented in the prior case.” United States v.
Brocksmith, 991 F.2d 1363, 1367 (7th Cir. 1993). Although the
United States and Illinois worked together in the investiga‐
tion of the oﬀense, joint law enforcement eﬀort does not mean
the prosecuting entities are in privity for the purposes of issue
preclusion. United States v. Davis, 906 F.2d 829, 834 (2d Cir.
1990). The United States is not bound by the state court’s res‐
olution of the suppression issue.
    We therefore AFFIRM the district court’s denial of Eymann
and Lyons’s motion to suppress, and thus the judgments en‐
tered against both defendants.
28                                       Nos. 19‐2090 & 19‐2101

    SYKES, Circuit Judge, concurring. I join Chief Judge
Wood’s opinion except for Part IIE, which concludes that
DHS Special Agent Harrington and his law‐enforcement
team lacked probable cause to arrest Lyons. In my view, the
oﬃcers had probable cause to arrest Lyons based on the
following facts known to them at the time:
        Lyons piloted at least one of the cross‐country, quick‐
         turn Cessna flights from California that prompted the
         call and email from DHS’s Air and Marine Operations
         Center to Agent Harrington. That flight—on the
         weekend of June 21, 2013—followed the same pattern
         as the one just a few weeks before on the weekend of
         May 24. During both trips, the plane landed at small,
         rural airports late at night, when the airports were
         otherwise closed, and used self‐service pumps to re‐
         fuel.
        Lyons’s wife owned the plane.
        When Harrington frisked Lyons, he felt what he
         thought was a wad of cash in his pocket. When asked
         about it, Lyons said it was an envelope containing
         $1,600. But the envelope actually contained $2,600 in
         cash. Misstating the amount by $1,000 was suspicious.
        Lyons said the cash was for fuel and expenses, but
         Harrington knew that the self‐service pumps at rural
         airports do not take cash. This added to the suspicion.
        Lyons’s fainting spell: Nervousness may be common
         in a police encounter, but fainting is unusual, as
         Harrington testified. This goes beyond the garden‐
         variety nervousness mentioned in United States v.
         Williams, 731 F.3d 678, 687 (7th Cir. 2013).
Nos. 19‐2090 & 19‐2101                                  29

   These facts—and the discovery of Eymann’s marijuana—
add up to probable cause. I agree, however, with Chief
Judge Wood’s analysis and application of the inevitable‐
discovery doctrine. So my disagreement on the probable‐
cause point means only that we end up in the same place for
two reasons.
30                                        Nos. 19‐2090 & 19‐2101

    HAMILTON, Circuit Judge, dissenting. I agree with several
portions of the majority opinion, but I differ from the majority
on three decisive issues. First, the initial police tactics in the
hotel parking lot amounted to unjustified arrests without
probable cause, not merely an investigative stop. Second,
even if the parking lot encounter were only an investigative
Terry stop, the police lacked reasonable suspicion at the outset
even to stop Eymann and Lyons. Reasonable suspicion
should require more than the curiosity of law enforcement of‐
ficers. Third, the majority errs in deciding the fact‐intensive
issue of inevitable discovery, which the district court did not
reach. I would vacate both defendants’ convictions and re‐
mand for fact‐finding on the government’s affirmative de‐
fense of inevitable discovery. I respectfully dissent.
I. The Arrests in the Hotel Parking Lot
    A reasonable person surrounded by the police in the hotel
parking lot that night would have understood that he was un‐
der arrest. In fact, the police officers testified in the state trial
court that Eymann and Lyons were under arrest from the mo‐
ment they were surrounded in the parking lot—at least one
officer explicitly, with the others confirming factual details in‐
dicating that the encounter was an arrest. Police Chief Wil‐
kinson testified:
       Q. Was Mr. Eymann arrested at that point
          [when the police cars pulled up behind their
          vehicle]?
       A. He was in custody, yes, sir.
   In response to a question about “arrest,” that answer can‐
not plausibly be explained, as the majority opinion does, as
having meant “only a Terry stop.” A year later, though, the
Nos. 19‐2090 & 19‐2101                                        31

officers changed their testimony in the federal district court.
This time, they claimed the initial detention was only a Terry
stop. But these experienced police officers knew the difference
between an arrest and a Terry stop when they testified in state
court. They were right the first time.
    The line between a Terry stop and an arrest is “not bright,”
United States v. Askew, 403 F.3d 496, 507 (7th Cir. 2005), but it
is exceedingly important. Terry recognized a “wholly differ‐
ent kind of intrusion upon individual freedom” based, for the
first time, on less than probable cause to believe the suspect
was engaged in crime. Terry v. Ohio, 392 U.S. 1, 26 (1968). If
courts allow law enforcement officers to cloak as “investiga‐
tory stops” what are really just arrests without probable
cause, all of us will have less liberty than the founders estab‐
lished for us in the Fourth Amendment.
    The majority concludes that the parking lot encounter was
a Terry stop “[b]ecause the officers used little show‐of‐force,
kept their questioning within reasonable bounds, and acted
consistently with an investigatory detention,” such that “a
reasonable person would not have understood that his free‐
dom was restrained to the degree associated with a formal ar‐
rest during the period before the handcuffing.” Ante at 16.
    I disagree. While there is no bright line between an arrest
and a Terry stop, “common sense and ordinary human expe‐
rience must govern.” United States v. Sharpe, 470 U.S. 675, 685
(1985). As many as nine officers in multiple marked cars
pulled in behind defendants’ car, blocking it in. At least two
cars were flashing their colored emergency lights. The armed
and uniformed officers, some in tactical gear and body armor,
then approached the defendants. A few moments later, an of‐
ficer took the defendants’ identification and did not return it.
32                                        Nos. 19‐2090 & 19‐2101

Eymann and Lyons were then separated before Eymann was
questioned. Chief Wilkinson confiscated the keys to the air‐
port courtesy car that the men had been driving. Common
sense and ordinary human experience should convince us
that this scene was not consistent with the notion of a brief
encounter “to ask you a few questions.”
    These facts are sufficiently similar to those of United States
v. Ienco, 182 F.3d 517 (7th Cir. 1999), to show an arrest: a sig‐
nificant show of force, overwhelming police presence, and
identification and keys taken and kept by the police. See id. at
525, citing Florida v. Royer, 460 U.S. 491, 501–02 (1983) (where
officers at airport identified themselves as narcotics agents,
told defendant that he was suspected of transporting narcot‐
ics, and asked him to accompany them to a police room, while
retaining his airline ticket and driver’s license without indi‐
cating in any way that he was free to depart, defendant was
effectively seized for purposes of Fourth Amendment), United
States v. Gonzalez, 763 F.2d 1127, 1131–32 (10th Cir. 1985) (“ar‐
rest” found where police held driver’s license, car registration
and title), and United States v. Miller, 589 F.2d 1117, 1127 (1st
Cir. 1978) (police officer’s retention of the defendant’s driver’s
license which prevented the defendant from lawfully driving
his car was more of an arrest than a mere investigatory stop).
We have also held that large numbers of armed police tend to
indicate that a defendant was in custody. See, e.g., United
States v. Slaight, 620 F.3d 816, 820 (7th Cir. 2010); United States
v. Borostowski, 775 F.3d 851, 860–61 (7th Cir. 2014).
   What happened here was distinct from the common police
practice of asking for and briefly inspecting identification
during a traffic stop, cf. Hiibel v. Sixth Judicial Dist. Court, 542
U.S. 177, 186 (2004), and United States v. Hensley, 469 U.S. 221,
Nos. 19‐2090 & 19‐2101                                         33

229 (1985). In such routine stops, most drivers expect to re‐
ceive their identification back within a few minutes. With no
driver’s licenses, and no expectation of getting them back any
time soon, and amid an overwhelming police presence, Ey‐
mann and Lyons were effectively under arrest from the out‐
set.
    Finally, I cannot overlook the testimony of Chief Wil‐
kinson in the state court hearing on the motion to suppress
(which was eventually granted, leading to this Plan‐B federal
prosecution). In the state court, the Chief testified that the en‐
counter with Eymann and Lyons in the hotel parking lot was
an arrest from the start. Chief Wilkinson is an experienced of‐
ficer who surely knew the difference between an arrest and a
Terry stop. In a hearing on the broad‐based motion to sup‐
press, he testified this was an arrest. (The Illinois State’s At‐
torney never even contested this point: he said in his closing
argument that “The state is not going to try and sit here and
argue that they weren’t in custody.”) I’m troubled by Chief
Wilkinson’s changed testimony on this critical point after the
prosecution lost the motion to suppress in state court. He was
right the first time.
    The government does not claim, and could not claim, that
the officers had probable cause to arrest Eymann or Lyons in
the opening moments of the encounter in the parking lot. This
was an arrest without probable cause, and all of the evidence
obtained through the unlawful arrest should have been sup‐
pressed.
II. No Reasonable Suspicion to Detain
   Even if the parking lot encounter were properly deemed
only an investigative Terry stop, it was unconstitutional. The
34                                      Nos. 19‐2090 & 19‐2101

officers had received information that they could reasonably
deem worth investigating. That information fell short, how‐
ever, of grounds to stop Eymann and Lyons at the hotel that
night and thus to deprive them of their liberty. The officers
needed “a reasonable suspicion, grounded in specific and ar‐
ticulable facts,” that the men had committed a felony or were
about to commit a crime. Hensley, 469 U.S. at 229; United States
v. Lopez, 907 F.3d 472, 478 (7th Cir. 2018). They did not have
it.
    The Air and Marine Operations Center (AMOC) analyst
passed on to officers that a single‐engine Cessna was worth
investigating further because it had made prior quick‐turn
trips and used self‐service fuel pumps late at night. Although
the analyst said that these attributes were “similar to previous
violators,” the analyst also told the officers that “the plane,
owner, and pilot [were] nonsuspect.” (Like the majority, I
give little weight to the California origins of the flights or to
the mistaken impression that the plane had flown into bad
weather.) In short, the AMOC information did not set Ey‐
mann, Lyons, or their plane apart from the pool of law‐abid‐
ing pilots who make quick‐turn trips or use self‐service fuel
pumps at night.
    It is critical to respect the difference between the quantum
of suspicion required to stop a suspect and what is required
merely to investigate. No more than interest or curiosity on the
part of the police is required to investigate. Neither is enough
to justify an investigative stop, intruding on a person’s liberty.
    To make a lawful stop, police “must be able to point to
specific and articulable facts which, taken together with ra‐
tional inferences from those facts, reasonably warrant that in‐
Nos. 19‐2090 & 19‐2101                                         35

trusion.” Terry, 392 U.S. at 21. Though law enforcement offic‐
ers are entitled to a certain amount of deference, courts must
still ensure that reasonable suspicion rests on an adequate ob‐
jective basis. See, e.g., id. at 21–22. Without an objective basis
giving rise to individualized suspicion, nothing sets apart
those reasonably suspected of criminal activity from those in‐
nocent Americans going about their daily lives—an outcome
that is inconsistent with the mandate of the Fourth Amend‐
ment. Kansas v. Glover, 140 S. Ct. 1183, 1190 (2020) (reasonable
suspicion does not “allow officers to stop drivers whose con‐
duct is no different from any other driver’s”); United States v.
Flores, 798 F.3d 645, 649 (7th Cir. 2015) (explaining that a “sus‐
picion so broad that [it] would permit the police to stop a sub‐
stantial portion of the lawfully driving public,” such as that
based on a license plate frame that obstructed a license plate
in exactly the same way as every other license plate frame,
was unreasonable).
    By definition, the grounds for a Terry stop can be less than
those required for probable cause. United States v. Arvizu, 534
U.S. 266, 274 (2002). But when the activity is much more likely
to be explained by innocent behavior than by criminal, the in‐
ference is weakened so that it cannot meet even the relatively
low standard for reasonable suspicion.
    Consistent with Glover, we have looked for a stronger con‐
nection between fact and inference than the officers had here.
In United States v. Paniagua‐Garcia, 813 F.3d 1013, 1014 (7th Cir.
2016), we held that a police officer’s observation that a driver
had his cell phone in hand with his head bent toward the
phone while driving was not enough to support reasonable
suspicion that he was breaking Indiana law by texting while
driving. The officer’s observations did nothing to separate the
36                                     Nos. 19‐2090 & 19‐2101

driver’s behavior from any of the many other lawful uses of a
cellphone while driving, all of which, except for texting, were
then legal under Indiana law. Id. (The statute, Ind. Code § 9‐
21‐8‐59, has since been amended effective July 1, 2020 to allow
only hands‐free use of cellphones while driving. See Pub. L.
100‐2020, § 3 (2020).)
    The government argues here that Eymann and Lyons fit
criteria for drug couriers. The problem is that the profile
criteria were so general and so likely to point to innocent
behavior that—without further investigation—it was not
possible to gauge the likelihood that a specific plane or person
was involved in criminal activity. AMOC itself told the
officers from the outset that “the plane, owner, and pilot
[were] nonsuspect.” Even the factors noted by the AMOC as
worthy of investigation were not probative of much. The
record sheds no light on how often “quick turnaround”
flights are evidence of crime. Private planes are expensive
items to leave idle, after all, and they make sense not just for
drug couriers but for anyone who does not want to be tied to
airline schedules and major airports. There are lots of lawful
reasons to fly from California to other parts of the country.
And using small, closed airports to refuel requires pilots to
leave a trail by paying for fuel with a credit card, and seems
to be common enough among law‐abiding pilots to support
the “courtesy car” practice allowing pilots to borrow cars on
the honor system.
    What the government here has called “reasonable suspi‐
cion” for Terry purposes was only interest or bare suspicion
that simply was not enough to justify a coercive, non‐volun‐
tary stop. Paniagua‐Garcia, 813 F.3d at 1015. We were con‐
cerned in Paniagua‐Garcia by how remote the likelihood of
Nos. 19‐2090 & 19‐2101                                         37

criminal activity was. We compared the case of a driver drink‐
ing from a coffee cup. The coffee could be spiked with alcohol,
or the driver could be driving on an expired license. Id. With‐
out more specific grounds for individual suspicion, however,
those possibilities could not justify a stop.
    American liberty requires us to enforce the difference be‐
tween grounds to investigate by non‐coercive means and rea‐
sonable suspicion to carry out a Terry stop. What judges and
lawyers blandly call “Terry stops” can be highly intrusive.
With the authority to stop comes the authority to require the
subject to submit to the stop, and to use reasonable force to
make him submit. United States v. Place, 462 U.S. 696, 702
(1983) (Terry implicitly acknowledged authority of police to
make forcible stop based on reasonable suspicion); Adams v.
Williams, 407 U.S. 143, 146 (1972) (upholding forcible stop
based on tip from reliable informant). Such situations can es‐
calate quickly to violence and even death. See, e.g., Tom v.
Voida, 963 F.2d 952, 954 (7th Cir. 1992) (attempt to make justi‐
fied Terry stop led to officer fatally shooting subject); Brown v.
City of Milwaukee, 288 F. Supp. 2d 962 (E.D. Wis. 2003) (Terry
stop based on mistaken identification resulted in permanent
injuries and pain).
    Here, when the officers encountered Eymann and Lyons,
as in Paniagua‐Garcia, they had information indicating at most
that criminal conduct was possible. It’s not surprising that
some small planes are used to transport drugs, but the record
tells us nothing about how suspicious the behavior that
AMOC observed was. By comparison, case law shows that
many drug couriers drive cars on long trips on interstate high‐
ways. That fact, without more, is not enough to justify a Terry
38                                      Nos. 19‐2090 & 19‐2101

stop on any car with out‐of‐state plates on an interstate high‐
way. Courts insist instead that stops of vehicles be based on
much more specific information, including violations of traf‐
fic laws.
    The facts here contrast sharply with a case cited by the
government, United States v. Latorre, 893 F.3d 744, 748, 751
(10th Cir. 2018), which affirmed the denial of a motion to sup‐
press. The police in Latorre knew of the private plane’s unu‐
sual flight pattern, but they also knew the pilot had a history
of arrests for drug possession and distribution. Most signifi‐
cant, the pilot was flying without using the required identifi‐
cation transponder. There may be legitimate reasons for that
last point—perhaps the transponder has suddenly stopped
working – but it is certainly suspicious. The Tenth Circuit held
that the three factors together supported reasonable suspicion,
and the lack of transponder was the most compelling. See id.;
see also Royer, 460 U.S. at 502 (officers had reasonable suspi‐
cion for initial Terry stop where drug courier paid for ticket in
cash under an assumed name). In this case, by contrast,
AMOC cited no behavior that indicated a desire to avoid de‐
tection. In fact, the opposite was true. When Eymann and Ly‐
ons stopped to refuel, they paid with a credit card that rec‐
orded the transaction.
    The patience shown by Officer McFadden in Terry itself is
also instructive here. Two men on the street caught his eye.
Terry, 392 U.S. at 5. At first, he could not say why they raised
his suspicion, so he waited and watched. He saw them pace
past and peer into a store many times, an activity that looked
to him like casing the store for a robbery. The officer contin‐
ued to watch. He saw the two men have a brief conversation
with a third man, who then left. The two men then resumed
Nos. 19‐2090 & 19‐2101                                          39

their activity in front of the store. The officer still did not at‐
tempt to detain them. He continued to investigate without
seizing anyone. As the two men began walking away, he fol‐
lowed them. When they met up with the third man once
again, Officer McFadden finally stopped them and found con‐
cealed weapons. Id. at 7. Terry thus showed the development
of the officer’s reasonable suspicion, starting from a vague
hunch that two men on the street were up to no good, to fi‐
nally observing enough suspicious actions that stopping them
had become reasonable. It was critical that the officer took the
time to observe something objectively suspicious before initi‐
ating his stop.
    As with the initial hunch in Terry, the officers who re‐
ceived AMOC’s information had enough reason to investi‐
gate, by watching. But unlike in Terry, the defendants here
demonstrated no behavior that was clearly suspicious. The
police here did not take the time to use the information from
AMOC to see if the subjects started behaving in unusual and
objectively suspicious ways. The officers here were much too
hasty. They moved in to detain Eymann and Lyons well be‐
fore they had grounds to set them apart from the general, law‐
abiding population. The officers violated the Fourth Amend‐
ment by detaining them.
    I do not suggest that the officers could not take any action
on the basis of the information from AMOC. The alert from
AMOC was to be on the lookout. It gave the officers a basis to
investigate—to observe the subjects and even to talk with
them if they were willing—but without (yet) restraining their
liberty. See United States v. Williams, 731 F.3d 678, 693 (7th Cir.
2013) (Hamilton, J., concurring) (anonymous call that a group
40                                     Nos. 19‐2090 & 19‐2101

of men outside a bar were showing each other their guns jus‐
tified a police response to investigate, but not to detain any‐
one without more reason to suspect wrongdoing when state
law allowed open possession of firearms).
    Stopping pilots and passengers based on only the infor‐
mation relied on here would allow the police to detain a sub‐
stantial portion of those flying lawfully. The information pro‐
vided by AMOC gave the officers reason to investigate fur‐
ther, but it fell short of providing the reasonable suspicion
necessary to restrain anyone’s movements. The entire case
against Eymann and Lyons was built on that flawed founda‐
tion.
III. Inevitable Discovery?
    The government argues that even if the arrest or stop was
unlawful, the evidence seized from the plane should be ad‐
mitted under the inevitable discovery doctrine. That doctrine
allows the government to rescue the fruits of an unlawful
search or seizure by showing, by a preponderance of the evi‐
dence, that the evidence would have been discovered through
lawful means independent from any illegal search or seizure.
United States v. Jones, 72 F.3d 1324, 1330 (7th Cir. 1995).
    The wording is important: would have been discovered, as
events actually unfolded, not hypothetically might have been
discovered under a different and idealized set of circum‐
stances. The government needs to show either that it would
have obtained a warrant or that it would have been able to act
under a valid exception to the warrant requirement. The dis‐
trict court did not decide or make findings of fact on the inev‐
itable discovery theory.
Nos. 19‐2090 & 19‐2101                                           41

    The majority forges ahead and makes its own factual find‐
ings on this fact‐sensitive issue. With respect, that’s a mistake.
First, inevitable discovery always asks for some degree of
counterfactual speculation. The government’s brief offers sev‐
eral hypotheticals as to how a dog might have been deployed
lawfully to sniff the plane, even absent the invalid arrest/Terry
stop and the defendants’ ensuing admissions. That argument
falls short of showing that a dog inevitably would have been
deployed to the plane. In fact, Chief Wilkinson conceded as
much when he said in the federal suppression hearing that he
would not have automatically deployed a drug‐sniffing dog
to the plane. Other officers testified differently, but this is not
a record where an appellate court should be making its own
findings of fact in the first instance.
     Second, in this case there are legitimate questions about
the use of this dog, his training, and his reliability. The state
courts have already found that the dog was not properly cer‐
tified at the time of these events. How does that affect the in‐
evitability of lawful discovery? Third, it is not clear that a war‐
rantless search of an airplane is subject to the same rules as a
warrantless search of an automobile.
    It is possible that officers could have called a judge in the
middle of the night to obtain a warrant after a positive alert
from a reliable drug‐sniffing dog, and it is true that warrants
are often granted on this basis. It is not at all clear on this rec‐
ord that the officers would have actually done so. The scene
suggests that officers had no real plan. Upon seeing Eymann
and Lyons leave the airport, a federal agent made a spur‐of‐
the‐moment decision to follow them in their courtesy car. All
of the agents and officers then left the airport, leaving the
plane unattended. Given the number of agents and officers
42                                             Nos. 19‐2090 & 19‐2101

who converged on the hotel parking lot, surely one or two
could have been assigned to a dog sniff of the plane if that
really had been a foregone conclusion. Instead, when the dog
was actually deployed, it was first sent to the hotel parking
lot, not the plane. Given how events actually unfolded, the
government must hypothesize that the officers would have:
(1) deployed a drug dog to the plane, (2) executed a proper
sniff, (3) gotten a reliable positive hit, (4) applied for a war‐
rant, and (5) waited for a warrant. There are too many uncer‐
tainties here for us to say confidently, at least without factual
findings, that the government can satisfy the strict require‐
ments of the inevitable discovery defense for an unlawful
search.
   The government also argues that a warrant would not
have been necessary because the automobile exception to the
warrant requirement would have covered a hypothetical
search of the plane based on a positive dog alert.1
    The automobile exception has a practical purpose: to allow
officers to search a car under the “exigent circumstances” in
which the vehicle is readily mobile. United States v. Castaldi,

     1Footnote 3 of the majority opinion criticizes the defendants for not
raising the automobile exception question until their reply briefs. On ap‐
peal, however, the question arose only in reply to the government’s reli‐
ance on inevitable discovery as an alternate ground to affirm. The district
court did not reach the inevitable discovery question, so defendants did
not need to address it in their principal briefs on appeal. It is now clear,
however, that affirmance of at least Lyons’s conviction depends on the in‐
evitable discovery theory. The majority’s point about limited briefing of
the issue thus only underscores the value of having the district court ad‐
dress this fact‐intensive question in the first instance. The only court to
have considered the issue until now, the Illinois trial court, rejected the
inevitable discovery theory for the search of the airplane.
Nos. 19‐2090 & 19‐2101                                        43

453 F.2d 506, 510 (7th Cir. 1971). Under that logic, the automo‐
bile exception has been extended to other kinds of vehicles
that are easy to drive away. See, e.g., California v. Carney, 471
U.S. 386, 393 (1985) (motor homes); United States v. Smith, 456
F. App’x 200, 209 (4th Cir. 2011) (travel trailer); United States
v. Navas, 597 F.3d 492, 501 (2d Cir. 2010) (tractor trailer).
    This plane was not necessarily so mobile as to have made
seeking a warrant impractical. The plane was locked, the of‐
ficers had its key, and it was located in a different place than
Eymann and Lyons at the time of their arrests. Moreover, an
airplane cannot be moved as quickly and easily as an automo‐
bile. General aviation airports are not as public as open road‐
ways. Planes cannot easily be lost in a stream of traffic, and
flights can be tracked. Refueling a plane is not as simple as
stopping a car at the next highway exit. It could not be easily
stolen or broken into, and it did not offer a ready means of
escape. In short, this plane was going nowhere without the
officers’ express direction.
    The automobile exception has also been justified by the di‐
minished expectation of privacy in an automobile. See, e.g.,
United States v. Matthews, 32 F.3d 294, 299 (7th Cir. 1994);
United States v. Markling, 7 F.3d 1309, 1319 (7th Cir. 1993) (au‐
tomobile exception applied to a car in a motel parking lot be‐
cause “[t]he considerations underlying the automobile excep‐
tion,” namely, the car’s ready mobility and the driver’s re‐
duced expectation of privacy, were present). Though air‐
planes and airways are also regulated, a private airplane may
offer much more privacy. An automobile is visible to the gen‐
eral public and any passerby. It has windows and a wind‐
shield that allow easy viewing of its driver, passengers, and
contents. The interior of a private plane in flight is not at all
44                                     Nos. 19‐2090 & 19‐2101

visible to the general public or even to people in other planes.
Planes are not subject to being pulled over the way that auto‐
mobiles are. There is little reason for pilots and passengers on
private planes to think that law enforcement or the general
public could easily access or see into their plane.
    I would not reach a conclusion on the government’s inev‐
itable discovery defense. The better course here would be to
remand these cases to the district court for factual findings in
the first instance, including thorough explorations of the
dog’s availability and reliability and whether the police could
have lawfully searched the airplane without a warrant.
