                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,              
                 Plaintiff-Appellee,
                v.                           No. 05-50165
RAMON RAMIREZ, aka Monserrat
Meza-Ramirez, aka Natividad                   D.C. No.
                                           CR-04-01054-ER-5
Ramirez, aka Manuel Clavo-
Barraza, aka Natividad Vidana
Ramirez,
              Defendant-Appellant.
                                       

UNITED STATES OF AMERICA,                   No. 05-50181
                 Plaintiff-Appellee,
                v.                            D.C. No.
                                           CR-04-01054-ER-4
JAVIER BELTRAN,
                                              OPINION
             Defendant-Appellant.
                                       
        Appeal from the United States District Court
           for the Central District of California
         Edward Rafeedie, District Judge, Presiding

                 Argued and Submitted
          August 17, 2006—Pasadena, California

                   Filed January 16, 2007

   Before: Alex Kozinski, Diarmuid F. O’Scannlain, and
              Jay S. Bybee, Circuit Judges.

              Opinion by Judge O’Scannlain;
              Concurrence by Judge Kozinski

                             533
                  UNITED STATES v. RAMIREZ              537


                        COUNSEL

Craig A. Harbaugh, Deputy Federal Public Defender, Los
Angeles, California, argued the cause for the defendants-
appellants. Maria E. Stratton, Federal Public Defender, and
Sean K. Kennedy, Deputy Federal Public Defender, were on
the briefs for Defendant-Appellant Beltran. Brad D. Leven-
son, Deputy Federal Public Defender, was on the reply brief.
Jerald Brainin, Los Angeles, California, filed a brief for
Defendant-Appellant Ramirez.

Gonzalo P. Curiel, Assistant United States Attorney, Los
Angeles, California, argued the cause for the plaintiff-
appellee. Debra Wong Yang, United States Attorney, and
Thomas P. O’Brien, Assistant United States Attorney, were
on the brief.
538               UNITED STATES v. RAMIREZ
                         OPINION

O’SCANNLAIN, Circuit Judge:

   In this criminal appeal we must decide whether the “collec-
tive knowledge” doctrine justifies a warrantless stop of an
automobile by one officer at the request of another officer
within the same police department.

                              I

                              A

   This case began with an event in which defendants-
appellants Ramon Ramirez and Javier Beltran were not actu-
ally involved. On July 8, 2004, police officers in Glendale,
California, stopped a Mercury Mountaineer with a California
license plate no. 560A975. Its driver was arrested. Officer
Kim Lawrence, a 14-year veteran of the Glendale Police
Department, ran her drug-detecting dog along and through the
vehicle, and the dog alerted to the scent of narcotics. Inside
the vehicle the police found a sophisticated secret compart-
ment in the rear cargo area that could be accessed by an elec-
tronic release located at the vehicle’s front center console.
Sergeant Jack Meier, head of the department’s vice/narcotics
detail, and Officer Joseph Allen, a 14-year veteran of the
department, witnessed the search.

                              B

   Ramirez and Beltran came to the attention of the Glendale
Police Department on July 20, 2004 when officers were con-
ducting surveillance at a residence located on Brussels Ave-
nue in Los Angeles. Led by Sergeant Meier, the officers
observed the same Mercury Mountaineer leave that residence.
It was driven by Beltran, while Ramirez sat in the passenger
seat. Officer Allen noted that the Mountaineer was registered
to another individual at a North Hollywood address; accord-
                    UNITED STATES v. RAMIREZ                     539
ing to Allen’s written declaration, he believed the vehicle was
so registered “to avoid detection by law enforcement while
drug trafficking.” Officers Lawrence and Allen followed the
vehicle as it traveled to a parking lot located on Rosecrans
Boulevard in the city of Paramount.

   At 12:30 p.m., Officers Lawrence and Allen observed a
second vehicle, a Chevrolet Silverado, arrive at the Rosecrans
parking lot. Two men got out of the Silverado and approached
the Mountaineer; one was carrying what appeared to be a
weighted-down gym bag.1 Ramirez and Beltran met with
these individuals near the front of the Mountaineer. Beltran
then took the gym bag, opened the rear driver-side door, and
placed the gym bag in the Mountaineer. Ramirez entered the
vehicle through that same door as Beltran walked around the
vehicle to enter through the front passenger-side door. Officer
Lawrence then saw the vehicle “rocking back and forth in [a]
manner consistent with someone forcibly moving the vehi-
cle.” The appellants exited the vehicle and assumed their orig-
inal positions—Beltran driving with Ramirez in the passenger
seat.

   During the surveillance at the parking lot, Sergeant Meier
received reports from Officers Allen and Lawrence regarding
the gym bag and its placement in the rear area of the Mercury
Mountaineer. Sergeant Meier knew that this is where the
sophisticated hidden compartment had been found on July 8.
He was also told that one of the occupants of the Silverado
had returned to that vehicle carrying a yellow manila-style
envelope or box. At that time, according to his written decla-
ration, Sergeant Meier “formed the opinion that the Mercury
was transporting narcotics in the hidden compartment.”

  Surveillance groups including Officer Lawrence followed
both vehicles as they left the parking lot in separate direc-
  1
   These individuals were Paul Villalba and Leonel Medina. They were
co-defendants with the appellants but are not parties to this appeal.
540                UNITED STATES v. RAMIREZ
tions. At approximately 1:30 p.m., Sergeant Meier issued a
request over the police radio that a uniformed officer make a
“traffic stop” of the Mercury Mountaineer as it was traveling
on the I-5 freeway. His declaration states that he opted for this
tactic “in order to avoid alerting the occupants of the Mercury
of an ongoing drug investigation and for officer safety rea-
sons.”

   Officer Daniel Hulben, a 26-year veteran of the department,
responded to Sergeant Meier’s request. Officer Hulben stated
in a written declaration that he “was aware that Sgt. Meier
was the head of a Vice/Narcotics detail, and [Hulben]
believed that [Meier’s] request related to an ongoing narcotics
investigation.” Officer Hulben drove onto the I-5 freeway and
observed the Glendale police surveillance units. Officers in
those vehicles pointed out the Mercury Mountaineer.

   Officer Hulben followed the Mountaineer for approxi-
mately half a mile. He observed Beltran, still driving the vehi-
cle, repeatedly looking in the rear-view mirror for up to five
seconds at a time. The vehicle was straddling two lanes with
both passenger-side tires crossing the stripes and box dots.

   At 1:36 p.m., Officer Hulben stopped the Mountaineer for
failing to drive within a single lane. See CAL. VEH. CODE
§ 21658. He spoke with Beltran, who produced a Mexican
driver’s license. Officer Hulben then placed Beltran under
arrest for driving without a California license, purportedly in
violation of California Vehicle Code § 12500(a). Three other
uniformed officers arrived to assist Officer Hulben. Ramirez
was not arrested at that time, but he was given a ride to the
police station.

   At 2:35 p.m., Officer Lawrence ran her drug-detecting dog
around and through the Mercury Mountaineer. The dog
alerted to the odor of narcotics in the rear interior area of the
vehicle. The police then searched the hidden compartment
and discovered eight kilograms of cocaine.
                   UNITED STATES v. RAMIREZ                  541
                               C

   On August 5, 2004, a federal grand jury returned an indict-
ment against Ramirez, Beltran, and three other individuals.
The indictment charged the appellants with conspiracy to pos-
sess with intent to distribute eight kilograms of a mixture or
substance containing a detectable amount of cocaine, in viola-
tion of 21 U.S.C. § 846. It named the July 20, 2004 incident
as the requisite “overt act” in the conspiracy.

  Ramirez and Beltran each filed a motion to suppress the
cocaine found in the vehicle. Senior United States District
Judge Edward Rafeedie conducted a suppression hearing on
October 26, 2004.

   The appellants challenged the validity of the traffic stop
and argued that Officer Hulben lacked personal knowledge of
the facts purportedly giving rise to probable cause for an auto-
mobile search. The district court considered the traffic stop
irrelevant; it noted that “the mere fact that this was communi-
cated over the radio to make a traffic stop suggests that it is
not the ordinary type of traffic stop.” Rather, in the court’s
view, the issue was simply whether there existed probable
cause for the search. The court applied the collective knowl-
edge doctrine, and considered the facts known to all of the
officers involved in the investigation and search. Finding
probable cause, the court denied both suppression motions
from the bench. Judge Rafeedie filed a written order on
November 19, 2004.

   Thereafter, Ramirez and Beltran reached plea agreements
with the government. They conditioned their guilty pleas on
the opportunity to appeal the district court’s denial of the sup-
pression motions.

  The district court sentenced each appellant to 120 months
imprisonment, a five-year term of supervised release, and a
542                   UNITED STATES v. RAMIREZ
special assessment of $100. The district court entered its judg-
ment and commitment orders on March 2, 2005.

  Ramirez and Beltran filed timely notices of appeal.

                                   II

   At the outset, Ramirez and Beltran contend that the exis-
tence of probable cause is irrelevant because the actual or sub-
jective purpose of Officer Hulben’s actions was to make a
“traffic stop” and that stop was invalid because lane strad-
dling is not illegal unless the driver interferes with other vehi-
cles. They also allege—and the government now concedes—
that the arrest of Beltran was improper because his Mexican
driver’s license qualified him to operate a motor vehicle in
California. In their view, the subsequent search of the vehicle
was the result of this improper arrest and, therefore, the
cocaine should be suppressed.

                                   A

   [1] We reject the notion that the subjective purpose of Offi-
cer Hulben’s traffic stop renders the probable cause inquiry
irrelevant. The Supreme Court has made clear that an officer’s
subjective thoughts play no role in the Fourth Amendment
analysis. Whren v. United States, 517 U.S. 806, 811-13
(1996). More specifically, the fact that officers acted on one
rationale “would not foreclose the [government] from justify-
ing [the search] by proving probable cause.” Florida v. Royer,
460 U.S. 491, 507 (1983); United States v. Willis, 431 F.3d
709, 715 (9th Cir. 2005) (“Whren stands for the proposition
that if the officers have probable cause to believe that a traffic
violation occurred, the officers may conduct a traffic stop
even if the stop serves some other purpose.”).2 Thus, it does
  2
    Further, there is no requirement that the traffic violation have been
related to the grounds upon which the officers could have stopped the
vehicle to search for contraband. Devenpeck v. Alford, 543 U.S. 146,
                      UNITED STATES v. RAMIREZ                        543
not matter that Officer Hulben was directed to make a “traffic
stop,” nor does it matter whether he had valid grounds to
make the traffic stop because of lane-straddling. If the officers
had probable cause, then the seizure and search of the vehicle
will be justified.

   We also reject the defendants’ argument that the cocaine
must be suppressed because Beltran’s arrest for driving with-
out a California driver’s license was invalid. Although the
government appears to concede that Beltran’s Mexican driv-
er’s license permitted him to operate a motor vehicle in Cali-
fornia, the issue is of no consequence because the arrest was
not a causal factor in the officers’ discovery of the cocaine.
The narcotics squad arrived shortly after the stop. Had Beltran
not been arrested, Officer Hulben could have simply detained
Beltran and Ramirez on the side of the road until the squad—
with their drug-sniffing dog in tow—arrived on the scene.
Thus, the officers would have discovered the drugs even if
Beltran had not been arrested. “[I]f not even the ‘but for’ test
can be met, then clearly the evidence is not a fruit of the prior
Fourth Amendment violation.” 6 WAYNE LAFAVE, SEARCH AND
SEIZURE: A TREATISE ON THE FOURTH AMENDMENT § 11.4(a), at
260 (4th Ed. 2004); see also United States v. Pulliam, 405
F.3d 782, 791 (9th Cir. 2005) (holding that an allegedly
invalid detention “simply did not contribute or lead to” the
discovery of a firearm). The stop and search of the Mercury
Mountaineer was in no way the fruit of Beltran’s arrest; the
search was based on previously gathered information, aimed
at establishing probable cause to search for contraband.

153-54 (2004) (rejecting this Circuit’s previous rule); see also United
States v. Cervine, 347 F.3d 865, 871 n.7 (10th Cir. 2003) (“Although we
can find no opinion that applies the collective knowledge doctrine to jus-
tify a search when the stop was based on an unrelated traffic violation, we
see no reason that the policies underlying the collective knowledge doc-
trine would not support such a use.”).
544                   UNITED STATES v. RAMIREZ
                                    B

   We must determine, therefore, whether probable cause
existed to search the vehicle. At the heart of that inquiry is the
“collective knowledge” doctrine. Ramirez and Beltran reject
the notion that the stop and search can be justified by proba-
ble cause arising from the collective knowledge of all the offi-
cers involved. As we discuss further below, they would place
two limitations on the doctrine which would render it inappli-
cable here: (1) a “coordinated-investigation” requirement; and
(2) a “minimal communication” requirement. In any case,
they further contend, Officer Hulben conducted only a “traffic
stop” and was not actually motivated by suspicion of drug
trafficking.

   The government’s position is that the collective knowledge
of the various officers involved was sufficient to establish
probable cause to believe that the Mercury Mountaineer con-
tained narcotics at the time it was stopped on July 20, 2004.
The government rejects the limitations appellants seek to
place on the collective knowledge doctrine and insists that
courts can look to the facts known by all officers involved,
even if those facts are not communicated to the officer mak-
ing an arrest or stop. The government further urges that we
not ignore the existence of probable cause to stop the vehicle
simply because Officer Hulben sought to establish an alterna-
tive ground for the stop.3

   [2] Ramirez and Beltran concede that Sergeant Meier and
his surveillance team had probable cause to search the vehicle
for contraband. Thus, if the facts known by those officers can
be imputed to Officer Hulben, the district court’s denial of the
suppression motions must be affirmed.
  3
   A district court’s denial of a motion to suppress is reviewed de novo,
while the factual findings underlying the denial of the motion are reviewed
for clear error. United States v. Gust, 405 F.3d 797, 799 (9th Cir. 2005).
                      UNITED STATES v. RAMIREZ                       545
   [3] Under the collective knowledge doctrine, we must
determine whether an investigatory stop, search, or arrest
complied with the Fourth Amendment by “look[ing] to the
collective knowledge of all the officers involved in the crimi-
nal investigation although all of the information known to the
law enforcement officers involved in the investigation is not
communicated to the officer who actually [undertakes the
challenged action].” United States v. Sutton, 794 F.2d 1415,
1426 (9th Cir. 1986). See generally 2 WAYNE LAFAVE, SEARCH
AND SEIZURE: A TREATISE ON THE FOURTH AMENDMENT § 3.5
(4th ed. 2004).4

                                   III

  Our prior decisions have applied the collective knowledge
doctrine in at least two situations.

                                   A

   The first situation is where law enforcement agents are
working together in an investigation but have not explicitly
communicated the facts each has independently learned.
Application of the collective knowledge doctrine has sparked
disagreement in such a circumstance, see Bailey v. Newland,
263 F.3d 1022, 1032 (9th Cir. 2001) (citing an inter-
jurisdictional conflict); United States v. Shareef, 100 F.3d
1491, 1503-04 (10th Cir. 1996) (same), perhaps because no
single law enforcement officer knows all of the facts neces-
sary to establish reasonable suspicion or probable cause, and
thus aggregation of facts is required.

  [4] In prior cases, however, we have been willing to aggre-
gate the facts known to each of the officers involved at least
“[w]hen there has been communication among agents.”
  4
    The collective knowledge doctrine is otherwise known as the “fellow
officer” rule. See, e.g., State v. Soldahl, 331 Or. 420, 426, 15 P.3d 564,
567 (2000).
546                   UNITED STATES v. RAMIREZ
United States v. Del Vizo, 918 F.2d 821, 826 (9th Cir. 1990);
accord United States v. Jensen, 425 F.3d 698, 704-06 (9th
Cir. 2005); United States v. Sandoval-Venegas, 292 F.3d
1101, 1105 (9th Cir. 2002). At the same time, we have
applied the collective knowledge doctrine “regardless of
whether [any] information [giving rise to probable cause] was
actually communicated to” the officer conducting the stop,
search, or arrest. United States v. Bertrand, 926 F.2d 838, 844
(9th Cir. 1991) (emphasis added); see also United States v.
Bernard, 623 F.2d 551, 560-61 (9th Cir. 1980) (looking to
collective knowledge “even though some of the critical infor-
mation had not been communicated to” the arresting officer);
Sutton, 794 F.2d at 1426 (same).

   [5] Even in this circumstance, the cases suggest a limited
requirement that there be a communication but not necessarily
the conveyance of any actual information among officers.5
This is a sensible rule; the purpose to be served by any
requirement of communication among the officers is simply
to “distinguish[ ] officers functioning as a team from officers
acting as independent actors who merely happen to be investi-
gating the same subject.” United States v. Terry, 400 F.3d
575, 581 (8th Cir. 2005); see also Bernard, 623 F.2d at 561
(“The officers involved were working in close concert with
each other and the knowledge of one of them was the knowl-
edge of all.” (internal quotation marks omitted)).
  5
    In Bernard, when we said that “some of the critical information had not
been communicated to” the arresting officer, 623 F.2d at 560-61 (empha-
sis added), we were not implying, as the appellants suggest, that other
pieces of information necessarily must have been communicated. Rather,
we were referring to some portion of the facts needed to constitute reason-
able suspicion or probable cause—the arresting officer knew some, but not
all, of the “critical information.” The missing pieces are imputed to him,
so long as he was working with the other officers, even though they were
not communicated.
                   UNITED STATES v. RAMIREZ                  547
                               B

   The facts of this case illustrate a second situation in which
the collective knowledge doctrine applies: where an officer
(or team of officers), with direct personal knowledge of all
the facts necessary to give rise to reasonable suspicion or
probable cause, directs or requests that another officer, not
previously involved in the investigation, conduct a stop,
search, or arrest. The application of the collective knowledge
doctrine to such situations has its roots in numerous decisions
of the Supreme Court and lower courts.

                               1

   In Whiteley v. Warden, 401 U.S. 560 (1971), a county sher-
iff put out a radio bulletin stating that two individuals were
wanted for breaking and entering. The bulletin provided the
suspects’ names, their descriptions, a description of the vehi-
cle they were likely driving, and the amount of money they
had stolen. A patrolman in another police department relied
on such information to make a warrantless arrest of the sus-
pects. Id. at 563-64. Although in Whiteley there was no show-
ing that the sheriff who issued the bulletin had facts sufficient
to establish probable cause to arrest, the Court assumed that
had the contrary been true, the patrolman’s arrest would have
been justified. It stated, “Certainly police officers called upon
to aid other officers in executing arrest warrants are entitled
to assume that the officers requesting aid offered the magis-
trate the information requisite to support an independent judi-
cial assessment of probable cause.” Id. at 568. Although in
Whiteley the bulletin provided factual information to the
arresting officer, the Court’s analysis seemed to take little
account of it.

   Then, in United States v. Hensley, 469 U.S. 221 (1985), a
police officer conducted an investigatory stop based upon
another police department’s “wanted flyer.” The flyer was
issued on the basis of articulable facts supporting reasonable
548                   UNITED STATES v. RAMIREZ
suspicion; it identified and described Hensley and gave the
date and location of an alleged robbery. 469 U.S. at 223. Cit-
ing Whiteley, supra, the Court explained:

      [W]hen evidence is uncovered during a search inci-
      dent to an arrest in reliance merely on a flyer or bul-
      letin, its admissibility turns on whether the officers
      who issued the flyer possessed probable cause to
      make the arrest. It does not turn on whether those
      relying on the flyer were themselves aware of the
      specific facts which led their colleagues to seek their
      assistance. In an era when criminal suspects are
      increasingly mobile and increasingly likely to flee
      across jurisdictional boundaries, this rule is a matter
      of common sense: it minimizes the volume of infor-
      mation concerning suspects that must be transmitted
      to other jurisdictions and enables police in one juris-
      diction to act promptly in reliance on information
      from another jurisdiction.

Id. at 231 (emphasis deleted and added). The Court did not
emphasize any details of the flyer; it was enough that the offi-
cer who issued the flyer knew facts supporting reasonable
suspicion. Id. at 234. In fact, the Court reversed the Sixth Cir-
cuit, which had rested its holding “on the omission from the
flyer of the specific and articulable facts which led the first
department to suspect [Hensley’s] involvement in a com-
pleted crime.” Id. at 230.

  Finally, in Illinois v. Andreas, 463 U.S. 765 (1983), the
Court considered a situation in which a Drug Enforcement
Agency agent, having already identified the illegal contents of
a container, reopened it following the defendant’s arrest but
before obtaining a search warrant.6 The Court rejected a hold-
  6
    A customs inspector had discovered quantities of marijuana inside a
large metal container, which had been shipped by air to the defendant. 463
U.S. at 767. The DEA agent, subsequently called to the scene, inspected
                      UNITED STATES v. RAMIREZ                        549
ing by the Appellate Court of Illinois “that [the DEA agent’s]
absence when the container was resealed by customs officers
somehow made less than certain his knowledge of the con-
tainer’s contents.” Id. at 772 n. 5. Citing Whiteley, supra, it
explained that “where law enforcement authorities are cooper-
ating in an investigation, as here, the knowledge of one is pre-
sumed shared by all.” Id. The Court did not mention the
substance of any communication from the customs officials to
the DEA agent regarding the contents of the container at the
time it was resealed. But see Bailey, 263 F.3d at 1031 (sug-
gesting that “[t]he facts of [Andreas] indicated that the DEA
agent knew of the contents of the package based on communi-
cations with other members of the investigation”).

                                    2

   [6] We have applied the collective knowledge doctrine in
similar circumstances. In Sutton, 794 F.2d at 1425-27, the
case in which we first recognized the collective knowledge
doctrine, we upheld an investigatory stop by a local deputy
sheriff where Customs officials had requested that local law
enforcement officers be dispatched to an airfield known for
narcotics smuggling. In assessing whether there was founded
suspicion of criminal conduct, we “combined” the facts
known to the Customs officials with those known to the dep-
uty sheriff—without discussing what facts, if any, had been
communicated by the former to the latter. Id. at 1427. We
explained that the collective knowledge doctrine applies “al-
though all of the information known to the law enforcement
officers involved in the investigation is not communicated to

the contraband. The container was resealed and then delivered to the
defendant, who was arrested after taking possession of it at his residence.
Id. Although the container was reopened prior to the authorities’ obtaining
a warrant, the Court affirmed the search, holding that “[n]o protected pri-
vacy interest remains in contraband in a container once government offi-
cers lawfully have opened that container and identified its contents as
illegal.” Id. at 771.
550                UNITED STATES v. RAMIREZ
the officer who actually makes the stop,” and we noted that
an officer may act “based in part on information or directions
from other law enforcement officials.” Id. at 1426 (emphasis
added).

   Similarly, in United States v. Mayo, 394 F.3d 1271 (9th
Cir. 2005), a police officer received a phone call from a
known informant, a manager at a motel in an area known for
narcotics activity. The motel manager informed the officer of
facts constituting reasonable suspicion: that several vehicles
were parked nearby; that the occupants got out and began
talking; that one of them handed another a package; and that
another wiped down the steering wheel of his vehicle and
walked away from the group. Id. at 1273 & n.1. The officer
then radioed a police dispatcher, who in turn notified another
officer that he should “investigate suspicious narcotics activi-
ty” at the motel. The dispatcher relayed only that directive
and a description of the cars involved. Id. at 1273, 1275 &
n.7. On those facts, we applied the collective knowledge doc-
trine and upheld the second officer’s detention and question-
ing of the defendant. Id. at 1275.

                               3

   Other circuits have applied the collective knowledge doc-
trine in nearly identical factual situations. In United States v.
Rodriguez, 831 F.2d 162 (7th Cir. 1987), agents of the DEA
had reasonable and articulable suspicion to stop the defen-
dant’s vehicle based on prior surveillance of narcotics activ-
ity. The DEA, however, asked local law enforcement to
conduct a “routine traffic stop” for them. Id. at 164. Although
the Seventh Circuit ultimately resolved the case on the basis
of inevitable discovery, id. at 167, it also noted the collective
knowledge doctrine’s application to the case as follows:

      [T]he detaining officer had a reasonable basis for
      believing the request to be well-founded—even
      though she did not personally know the facts giving
                   UNITED STATES v. RAMIREZ                  551
    rise to the suspicion. Unlike Hensley, here the auto-
    mobile to be stopped with its occupant was pointed
    out specifically by the requesting officer, and the
    detaining officer knew the requesting officer was
    coordinating a large investigation with local agen-
    cies. The state trooper was therefore merely acting as
    an “extension” or agent of the DEA agent and she
    could act on the DEA agent’s suspicions.

Id. at 166.

   In United States v. Ibarra-Sanchez, 199 F.3d 753 (5th Cir.
1999), another similar case, a DEA agent observed a beige
van coming and going from a house known for involvement
in narcotics trafficking. At one point, the agent witnessed sev-
eral men loading duffel bags into the van. Id. at 756-57. To
avoid revealing the existence of the investigation to the van’s
occupants, he called the El Paso Police Department to make
a stop of the vehicle. Id. at 757 & n.1. A dispatcher issued a
radio bulletin that a DEA agent had requested assistance in
stopping a beige van because it was possibly transporting
drugs or weapons. A police officer and SWAT team then
stopped the van. Id. at 757. The Fifth Circuit held that the
officers had reasonable suspicion to stop the van because the
DEA agent’s knowledge was imputed to them under the col-
lective knowledge doctrine. Id. at 759-60.

   [7] Lastly, in United States v. Burton, 288 F.3d 91 (3d Cir.
2002), a DEA task force used a confidential informant and
surveillance techniques to acquire probable cause to arrest the
defendant for narcotics trafficking. Id. at 97-99. The agents
followed the defendant from the scene of a narcotics transac-
tion, but they requested assistance in stopping his vehicle. A
uniformed police officer responded. Id. at 95. The Third Cir-
cuit held that the information known to the DEA task force
was sufficient; “the arresting officer need not possess an
encyclopedic knowledge of the facts supporting probable
cause, but can instead rely on an instruction to arrest delivered
552                UNITED STATES v. RAMIREZ
by other officers possessing probable cause.” Id. at 99 (cita-
tion omitted). Indeed, the court applied the collective knowl-
edge doctrine without any discussion of what information was
communicated to the arresting officer.

                               C

   The foregoing cases cut against the appellants’ view of the
collective knowledge doctrine. In each case, one officer (or
team of officers) had all of the necessary facts, and thus no
amassing of independently discovered facts was required. In
each case, the officer conducting the stop, search, or arrest
was given little more than an order or request; the investigat-
ing officer or agent simply provided a description of the sus-
pect, thus pointing out who was the target. In none of these
cases did the investigating officer relay to the second officer
the factual basis for his determination that reasonable suspi-
cion or probable cause existed.

   [8] Although Ramirez and Beltran concede that an investi-
gating officer need not convey all of the facts known to him,
they nonetheless insist that “the information conveyed to the
[officer conducting the stop, search, or arrest] must relate in
some meaningful way to suspected criminal activity.” Here,
they think probable cause is lacking because Sergeant Meier
relayed only a request for a “traffic stop” and failed to men-
tion anything about its purpose. But placing such a limitation
on the collective knowledge doctrine would go far beyond the
purpose of “distinguish[ing] officers functioning as a team
from officers acting as independent actors who merely happen
to be investigating the same subject.” Terry, 400 F.3d at 581.
Indeed, where one officer directs another to take some action,
there is necessarily a “communication” between those offi-
cers, and they are necessarily functioning as a team. Officer
Hulben was not investigating Ramirez and Beltran indepen-
dently; he acted only because of a communication from a fel-
low officer. See Shareef, 100 F.3d at 1503 n.4 (noting that
“[i]t is well-established that when an order to stop or arrest a
                      UNITED STATES v. RAMIREZ                       553
suspect is communicated to officers in the field, the underly-
ing facts constituting probable cause or reasonable suspicion
need not be communicated”).

   It is true that in some of our prior cases the investigating
officer suggested why the defendant should be seized, see,
e.g., Mayo, 394 F.3d at 1273 (noting that the arresting officer
was told “to investigate suspicious activity, possibly involv-
ing narcotics”), but at no time have we suggested that the con-
veyance of such information was affirmatively required.7
Ramirez and Beltran suggest no possible rationale for impos-
ing that kind of requirement, and none is apparent to us. Had
Sergeant Meier said explicitly that Ramirez and Beltran were
suspected of narcotics activity, such information would not
have brought Officer Hulben any closer independently to
knowing facts sufficient to constitute probable cause. We
would still have to impute facts known only to Sergeant Meier
and his team.

   Moreover, there is good reason to reject such a proposed
limitation:

      The accepted practice of modern law enforcement is
      that an officer often makes arrests at the direction of
      another law enforcement officer even though the
      arresting officer himself lacks actual, personal
      knowledge of the facts supporting probable
      cause. . . .
  7
   To the extent there was a substantive communication at issue in our
prior cases, we suggested only that such communication was sufficient,
not necessary, to invoke the collective knowledge doctrine. See Jensen,
425 F.3d at 704-06; United States v. $129,727.00 U.S. Currency, 129 F.3d
486, 489 (9th Cir. 1997); United States v. Valencia, 24 F.3d 1106, 1108
(9th Cir. 1994); Bertrand, 926 F.2d at 844. In fact, we made this explicit
in Bernard. See 623 F.2d at 561 (“We do not find, however, that this is
required, particularly where, as here, the agents were working in close
concert.”). Thus, we cannot agree with the district court’s analysis in
United States v. Newman, 265 F. Supp. 2d 1100, 1106-08 (D. Ariz. 2003).
554                   UNITED STATES v. RAMIREZ
         . . . The rule exists because, in light of the com-
      plexity of modern police work, the arresting officer
      cannot always be aware of every aspect of an inves-
      tigation; sometimes his authority to arrest a suspect
      is based on facts known only to his superior or asso-
      ciates.

Jensen, 425 F.3d at 704-05 (citations and internal quotation
marks omitted). The Supreme Court has shared these con-
cerns, specifically endorsing our view “ ‘that effective law
enforcement cannot be conducted unless police officers can
act on directions and information transmitted by one officer
to another and that officers, who must often act swiftly, can-
not be expected to cross-examine their fellow officers about
the foundation for the transmitted information.’ ” Hensley,
469 U.S. at 231 (quoting United States v. Robinson, 536 F.2d
1298, 1299 (9th Cir. 1976)).

   Accordingly, we reject the appellants’ view of the limita-
tions on the collective knowledge doctrine.8

                                   IV

   [9] We are satisfied that the collective knowledge doctrine
includes no requirement regarding the content of the commu-
nication that one officer must make to another. Where one
   8
     Ramirez and Beltran also suggest that to invoke the collective knowl-
edge doctrine, “all officers must be members of a coordinated criminal
investigation.” Of course, Officer Hulben clearly was part of a coordinated
effort—he acted on a request from Sergeant Meier. But their argument
seems to go further. They say that collective knowledge cannot apply
because “Officer Hulben did not participate in any way with either the sur-
veillance of [Appellants] or the Mountaineer. In fact, Officer Hulben was
not even assigned to the narcotics division; he worked as a motor officer
in the traffic division for the past 15 years.” This argument is without
merit, and it clearly conflates the two situations we distinguished above.
There is no requirement that Officer Hulben have been connected to or
involved in the prior investigation. See, e.g., Mayo, 394 F.3d at 1273-75.
                   UNITED STATES v. RAMIREZ                  555
officer knows facts constituting reasonable suspicion or prob-
able cause (sufficient to justify action under an exception to
the warrant requirement), and he communicates an appropri-
ate order or request, another officer may conduct a warrant-
less stop, search, or arrest without violating the Fourth
Amendment. Accordingly, appellant’s convictions are

  AFFIRMED.



KOZINSKI, Circuit Judge, concurring:

   I join Judge O’Scannlain’s opinion, but write separately to
emphasize what this case is not about. This is not a case
where the investigating officers ordered a fellow officer to
conduct a traffic stop because they lacked probable cause for
a narcotics stop. Sergeant Meier had probable cause to order
a narcotics stop, and that’s exactly what he did. He requested
that the arresting officer make it look like a “traffic stop” as
a safety measure, to prevent the risk of harm to a lone officer
trying to make a narcotics arrest before backups could arrive
on the scene. But that did not change the nature of the stop,
which remained—in substance—a narcotics stop.

   Concern for the officer’s safety was entirely justified
because the evidence suggested that the suspects were sea-
soned drug traffickers with access to sophisticated equipment
to ply their trade. It was not unreasonable for Sergeant Meier
to fear that the suspects might use force against the officer
who made the stop, had they realized the real reason for it.
Thus, disguising the stop as a “traffic stop” was a valid law
enforcement tactic calculated to ensure an officer’s safety.
The case would, of course, be quite different if an officer who
had no probable cause or reasonable suspicion were to con-
duct (or direct another officer to conduct) a traffic stop in the
hope of finding something illegal or delaying the suspect.
That kind of pretextual traffic stop is clearly prohibited by the
556             UNITED STATES v. RAMIREZ
Fourth Amendment. See United States v. Wallace, 213 F.3d
1216, 1220-21 (9th Cir. 2000).
