                              In the

    United States Court of Appeals
                For the Seventh Circuit
                    ____________________
No. 15-3044
MARCUS MUHAMMAD, et al.,
                                               Plaintiffs-Appellants,
                                v.

DEL PEARSON, Police Officer #16462,
                                                Defendant-Appellee.
                    ____________________

        Appeal from the United States District Court for the
          Northern District of Illinois, Eastern Division.
          No. 13-CV-1122 — Charles R. Norgle, Judge.
                    ____________________

   ARGUED NOVEMBER 8, 2017 — DECIDED AUGUST 17, 2018
               ____________________

    Before WOOD, Chief Judge, and FLAUM and HAMILTON, Cir-
cuit Judges.
    HAMILTON, Circuit Judge. When Oﬃcer Del Pearson and
other Chicago police oﬃcers executed a search warrant for
“apartment 1” at a Chicago address, there was a problem with
the warrant. Apartment 1 did not exist. The building con-
tained an apartment 1A and an apartment 1B. Pearson and the
other oﬃcers actually searched apartment 1A. They did not
ﬁnd the drugs and related items they were seeking.
2                                                  No. 15-3044

    The occupants of apartment 1A then ﬁled this suit against
Oﬃcer Pearson under 42 U.S.C. § 1983 for violating their
Fourth Amendment rights through unlawful entry and false
arrest. Both sides moved for summary judgment. The district
court denied plaintiﬀs’ motion and granted Pearson’s. We af-
ﬁrm the judgment but on narrow grounds. Law enforcement
oﬃcers who discover that a search warrant does not clearly
specify the premises to be searched must ordinarily stop and
clear up the ambiguity before they conduct or continue the
search. See Maryland v. Garrison, 480 U.S. 79, 86 (1987); United
States v. Kelly, 772 F.3d 1072, 1083 (7th Cir. 2014). If they do
not, they may lose the legal protection the warrant provides
for an invasion of privacy and accompanying restraints on lib-
erty.
   As we explain below, however, we conclude that sum-
mary judgment for the oﬃcer was appropriate here. Defend-
ant Pearson testiﬁed that he did not know there were two
apartments, including an apartment 1B, and he has oﬀered
undisputed, reliable, and contemporaneous documents con-
ﬁrming his after-the-fact testimony that the address searched
was in fact the correct target of the search authorized by the
ambiguous warrant. Summary judgment on the unlawful en-
try claims was correct. Also, Oﬃcer Pearson had arguable
probable cause to arrest plaintiﬀ Muhammad for suspected
drug traﬃcking, though Pearson quickly conﬁrmed that Mu-
hammad was not the right suspect and released him within
ﬁfteen minutes. Summary judgment based on qualiﬁed im-
munity was also correct on that unlawful arrest claim.
I. Factual and Procedural Background
   Our account of the facts applies the summary judgment
standard, relying on facts that are not genuinely disputed but
No. 15-3044                                                  3

giving plaintiﬀs, as the non-moving parties, the beneﬁt of con-
ﬂicts in the evidence and reasonable inferences from the evi-
dence. Zimmerman v. Doran, 807 F.3d 178, 182 (7th Cir. 2015),
citing Hardaway v. Meyerhoﬀ, 734 F.3d 740, 743 (7th Cir. 2013).
    Pearson applied for the warrant based on a tip from a
known and previously reliable informant. The aﬃdavit for
the warrant included the following information. In the three
months leading up to the tip, Pearson’s source had provided
information leading to three felony arrests and seizures of il-
legal drugs. The source told Pearson that she bought drugs
from a man named “Moe Moe” at “3236 E. 92nd St Apt#1.”
She described Moe Moe as a black male who was 25 to 30
years old, approximately 5’8” tall and medium build. Pearson
checked Chicago Police Department databases and discov-
ered that a man named Jamison Carr “used the address of
3236 E. 92nd St. on a previous arrest.” The aﬃdavit did not
indicate which apartment number was associated with that
arrest record. The source identiﬁed a photograph of Carr as
“Moe Moe.”
    The aﬃdavit also provided details about the transaction.
It said that the source met with Carr in apartment 1. He led
her into a back bedroom where she saw a “large frame semi-
auto blue steel handgun” on the table and purchased “four
small knotted baggies of crack cocaine.” The aﬃdavit also
stated that Oﬃcer Pearson and the source “personally drove
by the 3200 block of E. 92nd St” and that the source “pointed
to the apartment at 3236 E 92nd St. and identiﬁed it as the
apartment where [she] met the individual Jamison Carr a/k/a
‘Moe Moe’ and purchased the crack cocaine and observed the
above handgun.”
4                                                 No. 15-3044

    Based on that aﬃdavit, a state court judge issued a search
warrant—which Pearson also drafted—for “Jamison Carr,
a/k/a ‘Moe Moe’, a male black, 28 yoa, 5’08” tall, 140 lbs, me-
dium build, black hair,IR#1300675” and for premises de-
scribed as “a multi-unit building located at 3236 E. 92nd St.
Apt#1, Chicago, Illinois Cook County.” The search warrant
authorized the seizure of weapons, cocaine, drug parapher-
nalia, money and drug transaction records, and proof of resi-
dency as evidence of the crimes of unlawful use of a weapon
by a felon and drug possession.
    In his deposition, Oﬃcer Pearson provided more detail
about his investigation leading up to the warrant. He com-
piled an array of photographs from police databases of people
associated with the 92nd Street address and showed them to
the source. (The photo array is not in the record. Pearson tes-
tiﬁed he kept the ﬁle at his home and “probably” threw it
away.) The source identiﬁed Jamison Carr as “Moe Moe.” She
also identiﬁed Tracy Jones from a photograph and said Jones
lived in the target apartment with her pregnant daughter and
her daughter’s boyfriend, who sold crack cocaine from their
bedroom, where there was a gun.
    Turning to the contemporaneous documents indicating
that apartment 1A was the correct, intended target of the
search authorized by the warrant, Oﬃcer Pearson testiﬁed
that before he drafted the warrant aﬃdavit, he ran the license
plate on Tracy Jones’s car through the LEADS database. He
learned that the car was registered to Tracy Jones in apart-
ment 1A. The report linking Jones’s car to apartment 1A is
dated March 21, 2011—the day before the warrant was issued
and executed and, according to the aﬃdavit, the same day as
Pearson’s meeting with the source. Pearson also ﬁlled out a
No. 15-3044                                                  5

“deconﬂiction submission.” (Chicago police oﬃcers use this
document and procedure before executing search warrants to
ensure that other local or federal law-enforcement agencies
are not investigating the same address.) The deconﬂiction
submission is dated March 22, 2011, the date the warrant was
executed. It lists apartment 1A as the residential address of
Jamison Carr as the “target.” When Pearson executed the war-
rant, he had both the LEADS report for Jones’s car and the
deconﬂiction submission with him.
    A team of fourteen Chicago police oﬃcers executed the
search warrant late in the evening of March 22, 2011. They
pounded on the rear door of apartment 1A, said they were the
police, but received no response. Pearson was with a group of
oﬃcers who used a battering ram to try to break down the
rear door of apartment 1A. Another group of oﬃcers was sta-
tioned at the front door.
    Inside apartment 1A, the oﬃcers found plaintiﬀ Marcus
Muhammad in the bedroom with plaintiﬀ Micheala Jones,
who was pregnant. The oﬃcers did not ﬁnd a gun and did not
ﬁnd any drugs. The oﬃcers reported that they found ammu-
nition in the bedroom, but plaintiﬀs submitted aﬃdavits stat-
ing that they did not own, possess, or have any knowledge of
the ammunition. Plaintiﬀs claim the oﬃcers planted it.
    Oﬃcer Pearson noticed that Muhammad did not look like
the picture of Jamison Carr but testiﬁed that he “wasn’t sure.”
Muhammad denied that his nickname was Moe Moe, but he
did not have any identiﬁcation showing his correct name or
address (and that he was not Carr). Muhammad was seven
years younger and three inches shorter than Carr. Pearson ar-
rested Muhammad and took him to the station but released
6                                                    No. 15-3044

him after about 15 minutes, once he conﬁrmed that Muham-
mad was not Carr. That arrest is the basis of Muhammad’s
false arrest claim.
    The district court granted summary judgment for Oﬃcer
Pearson on all claims. It held that Pearson was entitled to qual-
iﬁed immunity on the unlawful entry claims because plain-
tiﬀs failed to show a violation of clearly established law. The
court granted summary judgment for Pearson on Muham-
mad’s false arrest claim, ﬁnding that Pearson had probable
cause to arrest him for possessing ammunition without a ﬁre-
arm owner’s identiﬁcation card. The district court dismissed
the other plaintiﬀs’ false arrest claims because they had failed
to show that oﬃcers detained them beyond what was permis-
sible in executing the warrant.
II. Analysis
    For civil damages claims under 42 U.S.C. § 1983 for viola-
tions of constitutional rights, the doctrine of qualiﬁed immun-
ity “shields oﬃcials from civil liability so long as their conduct
‘does not violate clearly established statutory or constitu-
tional rights of which a reasonable person would have
known.’” Mullenix v. Luna, 136 S. Ct. 305, 308 (2015) (per cu-
riam), quoting Pearson v. Callahan, 555 U.S. 223, 231 (2009).
“Put simply, qualiﬁed immunity protects ‘all but the plainly
incompetent or those who knowingly violate the law.’” Id.,
quoting Malley v. Briggs, 475 U.S. 335, 341 (1986).
    “To overcome a defendant’s invocation of qualiﬁed im-
munity, a plaintiﬀ must show: ‘(1) that the oﬃcial violated a
statutory or constitutional right, and (2) that the right was
‘clearly established’ at the time of the challenged conduct.’”
Green v. Newport, 868 F.3d 629, 633 (7th Cir. 2017), quoting
No. 15-3044                                                     7

Ashcroft v. al-Kidd, 563 U.S. 731, 735 (2011). We have discretion
to decide which element of the qualiﬁed immunity defense to
address ﬁrst. Pearson, 555 U.S. at 236. If the answer to either
question is no, the defendant oﬃcial is entitled to qualiﬁed
immunity. Gibbs v. Lomas, 755 F.3d 529, 537 (7th Cir. 2014). We
address ﬁrst the plaintiﬀs’ claims for unlawful entry and then
their claims for false arrest.
   A. Unlawful Entry Claims
    Under the Fourth Amendment, a search warrant must
“particularly describ[e] the place to be searched.” Failure to
do so renders the warrant a “general warrant,” which the
amendment clearly forbids. See Payton v. New York, 445 U.S.
573, 584 n.21 (1980) (tracing roots of particularity requirement
to colonists’ objections to writs of assistance). The particular-
ity requirement is satisﬁed if “the description is such that the
oﬃcer with a search warrant can with reasonable eﬀort ascer-
tain and identify the place intended.” Steele v. United States,
267 U.S. 498, 503 (1925).
   In this case, a judge found probable cause to search the
apartment where the informant told Oﬃcer Pearson she had
bought cocaine from “Moe Moe,” who had a gun at the time.
The problem is that the warrant authorized a search of “apart-
ment 1,” while the actual building had an apartment 1A and
an apartment 1B, but no apartment 1.
   Warrants with similar errors or ambiguities are not new.
When the police go forward with a search without checking
back with the issuing judge, litigation is likely. Sometimes
there is just a mistake in the papers. In other cases, oﬃcers
seeking search warrants cannot obtain accurate information
(especially about the interiors of multi-unit buildings), at least
8                                                    No. 15-3044

not without alerting the targets of the investigation. See, e.g.,
Maryland v. Garrison, 480 U.S. 79, 80 (1987) (warrant was for
“third ﬂoor apartment” but third ﬂoor had two apartments);
United States v. McMillian, 786 F.3d 630, 634 (7th Cir. 2015) (ty-
pographical error in warrant and aﬃdavit where target street
address for search was “6333” but detective typed “6633”);
United States v. Kelly, 772 F.3d 1072, 1076 (7th Cir. 2014) (war-
rant for “upper apartment” but building did not have upper
and lower apartments and was instead “bisected into front
and rear multi-story units”). And sometimes information is
lost in communications between two police oﬃcers. E.g., Jones
v. Wilhelm, 425 F.3d 455, 459 (7th Cir. 2005) (one oﬃcer ob-
tained warrant for “upstairs apartment on the right,” but ex-
ecuting oﬃcer realized that phrase described two apartments
because building had two staircases on opposite sides of
building).
    Oﬃcers executing warrants like these may violate the
Fourth Amendment if they know or should know, before ex-
ecution, that the warrant has an error or critical ambiguity
that risks a search of the wrong location. Garrison, 480 U.S. at
86. At the same time, typographical errors or other mistakes
will “not invalidate a warrant if the aﬃdavit otherwise iden-
tiﬁes the targeted premises in suﬃcient detail and there is no
chance that another location might be searched by mistake.”
McMillian, 786 F.3d at 640, citing Kelly, 772 F.3d at 1081.
    We approach this illegal entry claim through the lens of
qualiﬁed immunity and ask whether Oﬃcer Pearson’s actions
violated clearly established law. More precisely, since the dis-
trict court granted summary judgment for Pearson, the ques-
tion is whether the undisputed facts show that Pearson did
not violate clearly established law. “The Supreme Court has
No. 15-3044                                                     9

instructed that ‘clearly established law should not be deﬁned
at a high level of generality.’” Green, 868 F.3d at 633, quoting
White v. Pauly, 137 S. Ct. 548, 552 (2017) (per curiam). “While
a case directly on point is not required, ‘the clearly established
law must be particularized to the facts of the case.’” Id., quot-
ing White, 137 S. Ct. at 551 (internal quotation marks omitted).
“[G]eneral statements of the law” can give oﬃcers “fair and
clear warning.” White, 137 S. Ct. at 552, quoting United States
v. Lanier, 520 U.S. 259, 271 (1997). But “in the light of pre-ex-
isting law the unlawfulness must be apparent.” Id., quoting
Anderson v. Creighton, 483 U.S. 635, 640 (1987); see also District
of Columbia v. Wesby, 138 S. Ct. 577, 590 (2018) (“Of course,
there can be the rare ‘obvious case,’ where the unlawfulness
of the oﬃcer’s conduct is suﬃciently clear even though exist-
ing precedent does not address similar circumstances.”),
quoting Brosseau v. Haugen, 543 U.S. 194, 199 (2004) (per cu-
riam); Hope v. Pelzer, 536 U.S. 730, 741 (2002) (denying quali-
ﬁed immunity because handcuﬃng prisoner to hitching post
for hours in summer sun violated clearly established law and
noting that “oﬃcials can still be on notice that their conduct
violates established law even in novel factual circum-
stances”).
    With that qualiﬁed immunity standard in mind, we take a
closer look at Fourth Amendment law where search warrants
have errors or key ambiguities. We have held that oﬃcers ex-
ecuting a search warrant can rely on what they know and see
independent of the documents to make sure they search the
correct premises, at least where the circumstances show there
is no reasonable chance that the oﬃcers will search the wrong
location, meaning a location other than the one the issuing
magistrate authorized. E.g., McMillian, 786 F.3d at 640; Kelly,
772 F.3d at 1081; United States v. Johnson, 26 F.3d 669, 688 n.14,
10                                                  No. 15-3044

692 (7th Cir. 1994). As McMillian makes clear, other circuits
have long agreed. See, e.g., United States v. Gahagan, 865 F.2d
1490, 1497–98 (6th Cir. 1989) (collecting cases and aﬃrming
denial of motion to suppress); United States v. Garza, 980 F.2d
546, 552 (9th Cir. 1992); United States v. Burke, 784 F.2d 1090,
1092–93 (11th Cir. 1986) (reversing grant of motion to sup-
press; despite mistakes in address in warrant, executing oﬃc-
ers knew enough to know which premises should be
searched); United States v. Turner, 770 F.2d 1508, 1511 (9th Cir.
1985) (aﬃrming denial of motion to suppress; despite mis-
taken house number in warrant, executing oﬃcers could rely
on their knowledge to search correct premises).
    The plaintiﬀs rely heavily on Jones v. Wilhelm, where we
reversed a grant of qualiﬁed immunity for an oﬃcer who ex-
ecuted an ambiguous warrant despite knowing that its de-
scription of the place to be searched described two diﬀerent
apartments. 425 F.3d at 462–63 (oﬃcer knew, based on prior
surveillance, that building contained two staircases on oppo-
site sides of building, rendering description of the “upstairs
apartment on the right” ambiguous). We wrote in Jones that
the Fourth Amendment prohibited the oﬃcer “from applying
his earlier surveillance and subsequent deductions to resolve
the warrant’s ambiguity rather than presenting those obser-
vations to a magistrate for determination.” Id. at 463.
   Our opinion in Jones recounted the police mistakes in that
case. One oﬃcer received a tip from an informant that a
named person in a second-ﬂoor apartment was manufactur-
ing methamphetamine. That oﬃcer obtained a warrant to
search not the named person’s apartment but “the upstairs
apartment on the right.” He then gave that warrant to another
oﬃcer who had been watching pedestrian traﬃc to the second
No. 15-3044                                                   11

ﬂoor of the building. That oﬃcer, defendant Wilhelm in the
case, did not go back to the issuing court (and the oﬃcer who
had developed the probable cause information) to clear up the
ambiguity before carrying out the search. Instead, he seems to
have made his best guess about whether “the upstairs apart-
ment on the right” was to be chosen from the viewpoint of the
front door or the rear door. He chose wrongly and searched
the apartment that had not been the subject of the informant’s
tip. 425 F.3d at 463–64.
    Search ﬁrst, check later, is not a sound policing strategy.
Jones teaches that oﬃcers need to read the warrant before ex-
ecuting it, and they should call a judge if there is a discrep-
ancy between the aﬃdavit and the warrant. See, e.g., McMil-
lian, 786 F.3d at 634 (oﬃcer on scene called judge after notic-
ing error in address listed on warrant and aﬃdavit). If they
do not, they risk both personal civil liability and suppression
of evidence in any criminal prosecution.
    This case, however, is diﬀerent from Jones in a critical way.
Unlike the oﬃcer in Jones, who knew there were two apart-
ments, knew that the warrant was ambiguous, and essentially
took his best guess about which one to search, Oﬃcer Pearson
testiﬁed that when he applied for the warrant he did not know
there was an apartment 1B in the building. He also testiﬁed
that the omission of “A” from the warrant was a clerical omis-
sion. Pearson used his knowledge of the case, including infor-
mation from his source, to search the correct apartment, the
one for which he had probable cause.
   So Oﬃcer Pearson relies on the line of cases cited above
that allow executing oﬃcers to rely on what they know to
make sure they search the correct locations, despite errors or
ambiguities in search warrants. The critical question for this
12                                                 No. 15-3044

case is whether it was proper to resolve Pearson’s defense in
his favor on summary judgment. In civil litigation about
searches that turned out to involve mistakes or ambiguities in
warrants, there can be plenty of room for material factual dis-
putes about what the executing oﬃcers actually knew and
did. Parties and courts can reasonably question the credibility
of oﬃcers’ after-the-fact attempts to explain away their mis-
takes. Such cases may well present factual issues that require
a full trial to resolve.
    In this case, however, summary judgment was justiﬁed.
Oﬃcer Pearson has oﬀered undisputed evidence, in the form
of reliable, contemporaneous documents, conﬁrming that the
correct target apartment—the one he intended to search and
had probable cause to search—was apartment 1A. The
LEADS report (dated the day before the warrant) and the de-
conﬂiction submission (dated the same day the warrant was
executed) both listed apartment “1A” as the target of the
search. Those documents remove reasonable grounds for dis-
puting Pearson’s claim that he used his knowledge to ensure
that he searched the intended location.
    This contemporaneous evidence distinguishes this case
from others where we held that oﬃcers could not have con-
cluded that a plaintiﬀ’s apartment was the appropriate target
of the search warrant. E.g., Jacobs v. City of Chicago, 215 F.3d
758, 767–71 (7th Cir. 2000) (reversing grant of defendant’s mo-
tion to dismiss and denying qualiﬁed immunity where rea-
sonable oﬃcer could not have concluded plaintiﬀ’s apartment
was target of search and where there was “no indication that
the oﬃcers were certain that plaintiﬀs’ apartment was the
proper subject of the search”; warrant was for entire building
No. 15-3044                                                   13

but building actually consisted of three apartments with sep-
arate entrances).
    The reliable, contemporaneous documents avoid the dis-
putes and concerns that arise when “an executing oﬃcer is the
sole source of information about the location of the premises
to be searched.” See United States v. Lora-Solano, 330 F.3d 1288,
1294 (10th Cir. 2003). The documents conﬁrm that here there
was no substantial risk of searching by mistake someplace
other than the target. As in Kelly, that risk was further reduced
by the fact that only one apartment was accessible from the
rear door that Pearson entered. See Kelly, 772 F.3d at 1083
(“The oﬃcers limited their search to the targeted apartment
and, because only one apartment was accessible from the door
through which they entered the building, there was no risk
that they might inadvertently have searched the wrong unit.”)
(footnote omitted). That distinction means that, in these lim-
ited circumstances, Oﬃcer Pearson is entitled to qualiﬁed im-
munity on summary judgment.
    The contemporaneous documents make Pearson’s quali-
ﬁed-immunity defense stronger than the oﬃcer’s in Jones.
They objectively indicate that Oﬃcer Pearson “did not choose
to search plaintiﬀs’ apartment at random or maintain willful
ignorance of which apartment” to search, Jones, 425 F.3d at
470 (Flaum, J., concurring in part and dissenting in part) (in-
ternal quotation marks omitted), and in the language of the
Jones majority, Pearson did not realize there were two apart-
ments and try to use his observations to make his best guess
about which was the correct target, see id. at 465–66. In this
case, the documents provide contemporaneous support for
Pearson’s testimony that he searched the apartment to which
14                                                  No. 15-3044

the source pointed and for which the issuing judge had found
probable cause.
    Given the case law that allows an executing oﬃcer to use
his or her own knowledge to resolve ambiguities, at least
where there is no chance that the wrong location might be
searched by mistake, see McMillian, 786 F.3d at 640, citing
Kelly, 772 F.3d at 1081, and the contemporaneous documenta-
tion that corroborates Pearson’s testimony, we aﬃrm the dis-
trict court’s grant of summary judgment. Plaintiﬀs have not
identiﬁed a precedent that should have alerted Oﬃcer Pear-
son that he could not proceed to search the apartment that he
knew, beyond reasonable dispute, was the intended target.
See, e.g., Abbott v. Sangamon County, 705 F.3d 706, 723–24 (7th
Cir. 2013), citing Wheeler v. Lawson, 539 F.3d 629, 639 (7th Cir.
2008). On that ground, we aﬃrm summary judgment for
Pearson on the entry claims based on qualiﬁed immunity.
     B. False Arrest Claims
    Plaintiﬀs base their false arrest claims on two theories.
Tracy, Terrance, and Micheala Jones claim that they were de-
tained while the police were executing an invalid search war-
rant. Their claims fail for the same reasons Pearson is entitled
to qualiﬁed immunity on the unlawful entry claim, which was
also based on the challenge to the validity of the search war-
rant. When police are executing a search warrant, the Fourth
Amendment does not forbid them from detaining the occu-
pants of the premises during the search. See Muehler v. Mena,
544 U.S. 93, 98–100 (2005) (vacating and remanding denial of
qualiﬁed immunity), citing Michigan v. Summers, 452 U.S. 692,
705 (1981).
No. 15-3044                                                      15

   Muhammad’s claim is diﬀerent. He was actually arrested
and taken to the police station after the search was completed.
He was released after ﬁfteen minutes.
    “Probable cause is an absolute bar to a claim of false arrest
asserted under the Fourth Amendment and section 1983.”
Stokes v. Board of Education of City of Chicago, 599 F.3d 617, 622
(7th Cir. 2010), citing McBride v. Grice, 576 F.3d 703, 707 (7th
Cir. 2009) (aﬃrming summary judgment for defendant police
oﬃcer). “Probable cause exists if, at the time of the arrest, the
facts and circumstances within the defendant’s knowledge
‘are suﬃcient to warrant a prudent person, or one of reason-
able caution, in believing, in the circumstances shown, that
the suspect has committed ... an oﬀense.’” Id., quoting Chelios
v. Heavener, 520 F.3d 678, 686 (7th Cir. 2008) (reversing sum-
mary judgment for arresting oﬃcer).
    The probable-cause standard is objective and “relies on
the common-sense judgment of the oﬃcers based on the to-
tality of the circumstances.” Jackson v. Parker, 627 F.3d 634, 638
(7th Cir. 2010), quoting United States v. Reed, 443 F.3d 600, 603
(7th Cir. 2006). Probable cause “deals with probabilities and
depends on the totality of the circumstances.” Wesby, 138 S.
Ct. at 586, quoting Maryland v. Pringle, 540 U.S. 366, 371 (2003).
Probable cause “is ‘a ﬂuid concept’ that is ‘not readily, or even
usefully, reduced to a neat set of legal rules,’” id., quoting Illi-
nois v. Gates, 462 U.S. 213, 232 (1983). “It ‘requires only a prob-
ability or substantial chance of criminal activity, not an actual
showing of such activity.’” Id., quoting Gates, 462 U.S. at 243,
n.13.
   The district court granted summary judgment on the the-
ory that Pearson had probable cause to arrest Muhammad for
16                                                  No. 15-3044

possessing ammunition without a ﬁrearm owner’s identiﬁca-
tion card, a violation of 430 ILCS 65/2(a)(2). That was incor-
rect, at least on a motion for summary judgment. Plaintiﬀs
designated evidence that creates a genuine fact issue as to
whether the police planted the ammunition. Pearson testiﬁed
that the oﬃcers found bullets in Micheala’s bedroom, but
plaintiﬀs ﬁled aﬃdavits testifying that they did not own, pos-
sess, or have any personal knowledge of the ammunition the
oﬃcers claim to have found in the apartment. That conﬂicting
evidence presents a factual dispute that cannot be resolved on
a motion for summary judgment.
    Nevertheless, Oﬃcer Pearson had arguable probable
cause to arrest Muhammad for the drug oﬀense associated
with the source’s tip. An arrest is constitutional if it is made
with probable cause for an oﬀense, even if the arresting of-
ﬁcer’s stated or subjective reason for the arrest was for a dif-
ferent oﬀense. See Devenpeck v. Alford, 543 U.S. 146, 153 (2004).
Qualiﬁed immunity is available if there is “arguable probable
cause” for the arrest. See Hunter v. Bryant, 502 U.S. 224, 227–
28 (1991) (reversing denial of qualiﬁed immunity); Humphrey
v. Taszak, 148 F.3d 719, 725 (7th Cir. 1998) (same).
    Oﬃcer Pearson had arguable probable cause to arrest Mu-
hammad for possessing cocaine with intent to deliver, a vio-
lation of 720 ILCS 570/401, even though he turned out to be
the wrong person. The undisputed facts show the following.
Before entering apartment 1A, Pearson had probable cause to
believe that a black male named Jamison Carr had been sell-
ing drugs from the apartment, that the man had a ﬁrearm he
kept visible for drug deals, and that the man in question had
a pregnant girlfriend. (The detail about the pregnant girl-
friend is from Pearson’s deposition, not the complaint for the
No. 15-3044                                                   17

search warrant, but we see no basis for a genuine dispute
about the point.) Upon entering the apartment, Pearson en-
countered in the bedroom a black male with a pregnant girl-
friend. That man denied that his nickname was “Moe Moe”
and denied that he was Carr, but he did not have identiﬁca-
tion to prove who he was or where he lived. Muhammad was
a few years younger and about three inches shorter than Carr.
While on the scene in the apartment, Pearson thought Mu-
hammad did not look like the picture of Carr that he had, but
testiﬁed that he “wasn’t sure.”
    This information was not enough to convict Muhammad,
of course, but a reasonable oﬃcer in Pearson’s situation could
have found that he had probable cause to arrest Muhammad,
at least long enough to ﬁgure out deﬁnitively whether he was
the right person or not. Under these circumstances, especially
where Muhammad had no identiﬁcation with him, a reason-
able oﬃcer could have suspected that Muhammad might be
lying about his identity. See generally Wesby, 138 S. Ct. at 587
(reasonable for oﬃcers investigating unlawful entry to infer
partygoers lied because they claimed to be attending a bache-
lor party but could not identify the bachelor or who had in-
vited them), citing Devenpeck, 543 U.S. at 149, 155–56; see also
Hill v. California, 401 U.S. 797, 803 (1971) (“aliases and false
identiﬁcations are not uncommon”). That uncertainty about
Muhammad’s identity points toward qualiﬁed immunity.
   A reasonable oﬃcer can have probable cause even if she
turns out to be mistaken, Stokes, 599 F.3d at 622, citing Chelios
v. Heavener, 520 F.3d 678, 686 (7th Cir. 2008), and Kelley v.
Myler, 149 F.3d 641, 646 (7th Cir. 1998), and even if a witness
misidentiﬁes the target, Gramenos, 797 F.2d at 439 (“Probable
cause does not depend on the witness turning out to have
18                                                 No. 15-3044

been right; it’s what the police know, not whether they know
the truth, that matters.”). Discrepancies between a witness’s
description and an oﬃcer’s observation of the suspect are not
unusual and do not automatically negate probable cause. See
Pasiewicz v. Lake County Forest Preserve District, 270 F.3d 520,
524 (7th Cir. 2001) (oﬃcers had probable cause to arrest man
who did not exactly match witnesses’ description but “bore a
fair resemblance”). The Fourth Amendment “demands rea-
sonableness, not perfection.” Id. at 525.
    Plaintiﬀs point out that Oﬃcer Pearson based Muham-
mad’s arrest on some facts about the informant’s tip that do
not appear in the aﬃdavit for the search warrant. Aﬃdavits
for warrants are not required to include all facts known to the
oﬃcer, and the focus of the aﬃdavit was the search, not the
arrest of Carr. Muhammad has not presented a genuine issue
of material fact disputing Pearson’s deposition testimony
about the informant’s information about the pregnant girl-
friend or Pearson’s uncertainty about Muhammad’s identity
and residence. Accordingly, Oﬃcer Pearson had at least argu-
able probable cause to arrest Muhammad and is entitled to
qualiﬁed immunity for his arrest.
     The judgment of the district court is
                                                  AFFIRMED.
