                    FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

RAYMOND TORRES; MARIA ELVA               
ALMADOR-TORRES,
               Plaintiffs-Appellants,
                 v.
                                                No. 06-55817
CITY OF LOS ANGELES; LOS
ANGELES POLICE DEPARTMENT;                       D.C. No.
                                              CV-05-04171-RGK
BRAD ROBERTS, LAPD Detective;
JENNIFER HICKMAN, LAPD                           OPINION
Detective; STEVE PARK, LAPD
Detective; F. RAINS, LAPD
Detective,
              Defendants-Appellees.
                                         
        Appeal from the United States District Court
           for the Central District of California
        R. Gary Klausner, District Judge, Presiding

                    Argued and Submitted
           February 12, 2008—Pasadena, California

                     Filed August 26, 2008

       Before: Betty B. Fletcher and N. Randy Smith,
    Circuit Judges, and Samuel P. King,* District Judge.

                 Opinion by Judge B. Fletcher




   *The Honorable Samuel P. King, Senior United States District Judge
for the District of Hawaii, sitting by designation.

                               11723
                 TORRES v. CITY OF LOS ANGELES             11727


                          COUNSEL

Nelson E. Brestoff (argued), Moskowitz, Brestoff, Winston &
Blinderman, LLP, Valencia, California, Julia A. Follansbee,
Follansbee & Associates, Bend, Oregon, for the plaintiffs-
appellants.

Rockard J. Delgadillo, Janet G. Bogigian, Amy Jo Field
(argued), Los Angeles City Attorney’s Office, Los Angeles,
California, for the defendants-appellees.


                           OPINION

B. FLETCHER, Circuit Judge:

   In 2004, plaintiff Raymond Torres, who was then 16 years
old, was arrested, without a warrant, on charges of murder
and attempted murder. After 162 days of incarceration, Torres
was released when the district attorney dismissed the charges
against him. Following his release, Torres and his mother
(“Plaintiffs”) brought a civil rights action against the City of
Los Angeles, the Los Angeles Police Department (“LAPD”),
and four LAPD detectives (“Defendants”), seeking damages
under both federal and state law. After granting summary
judgment to the City of Los Angeles and the LAPD, the dis-
trict court denied two of Plaintiffs’ motions in limine and,
after all of the parties had presented their evidence to the jury,
granted the remaining Defendants’ motion for judgment as a
matter of law. Plaintiffs appeal the grant of the motion for
judgment as a matter of law as well as the rulings on the
motions in limine. We affirm in part, reverse in part, and
remand.
11728               TORRES v. CITY OF LOS ANGELES
                                     I.

   The charges leading to Torres’ arrest arose from a gang-
related shooting in Los Angeles on August 11, 2004. On that
day, Josue Santillan, a member of the Canoga Park Alabama
street gang (“CPA gang”), was driving a car that contained
four other passengers: Diana Hernandez, Santillan’s girl-
friend, who was seated in the front right passenger seat; Joel
Castaneda, who was seated in the back seat directly behind
Hernandez; and two other persons, at least one of them male,
who were also seated in the back seat.1 At one point Santillan
drove by a park in the Reseda area, where, according to Her-
nandez and other witnesses, the male passengers flashed gang
hand signs and shouted challenges at members of the Reseda
street gang who were in the park. Santillan then drove away,
but the members of the Reseda gang gave chase in a car of
their own. When the Reseda gang members’ car pulled along-
side the car driven by Santillan, Castaneda fired several
rounds from a semiautomatic pistol at the Reseda gang mem-
bers’ car, killing the driver and wounding another passenger.

   Detectives Roberts, Hickman, Park and Rains investigated
the shooting. On August 25, 2004, two weeks after the shoot-
ing, Detectives Roberts and Hickman questioned Hernandez
about the shooting. Hernandez identified Santillan as the
driver and Castaneda as the shooter, and both were subse-
quently arrested. Hernandez also expressed her belief that all
the male passengers were probably members of the CPA
gang.

   Detectives Roberts and Hickman asked Hernandez about
  1
    Hernandez, who was the detectives’ main source of information about
the shooting, gave different accounts of who was in the car other than her-
self, Santillan and Castaneda. At first she stated that only one other per-
son, a male, was in the car; later she stated that two other persons were
in the car, one male and one female; and later still she stated that only two
other males were in the car.
                   TORRES v. CITY OF LOS ANGELES                  11729
the third male passenger who had been sitting directly behind
Santillan. Hernandez told the detectives that she had never
seen him before, that she did not know his name, and that she
did not remember him well because she had not been paying
attention to him. However, Hernandez was able to describe
this third male passenger as Hispanic, 15 or 16 years old, with
a complexion darker than hers, and very overweight. Her-
nandez also stated that he had some hair. She further
described him as having worn a white T-shirt, blue shorts, and
white tennis shoes. Detective Roberts acknowledged at trial
that Hernandez’s description was “too generic to go anywhere
with it.”

   On September 23, 2004, six weeks after the shooting, the
detectives obtained several additional pieces of information in
their investigation of the third male passenger, which led them
to arrest Torres that same day.

   First, Detective Hickman spoke to Danny Steinberg, a
school police officer assigned to El Camino High School.
Previously, Steinberg had been questioned by an LAPD Juve-
nile Officer, Marie Lamar, about an outstanding suspect in a
murder case. Officer Lamar had described the suspect as a
short and heavy-set Hispanic male with a shaved head who
was “dressed down gang-style.”2 Steinberg had informed
Officer Lamar that her description matched a student at El
Camino—Torres—and that Torres had recently begun hang-
ing out with gang members at El Camino and had begun
“dressing down as a gangster” and shaving his head. On Sep-
tember 23, Steinberg repeated the same information to Detec-
tive Hickman. There was conflicting testimony at trial,
however, as to whether Steinberg also told Officer Lamar and
Detective Hickman that Torres had “recently been jumped
  2
    The record does not reveal how Officer Lamar had come to believe that
the third male passenger had a shaved head and was “dressed down gang-
style.”
11730           TORRES v. CITY OF LOS ANGELES
into the CPA gang,” i.e., that Torres had become a member
of the gang.

   Second, Detectives Hickman and Roberts spoke to an offi-
cial at El Camino high school, Mark Pomerantz. Pomerantz
gave the detectives two color photos of Torres, one older, in
which Torres is shown with short dark hair, and the other
taken that morning at the detectives’ request, in which Torres
is shown with a shaven head. In addition, Pomerantz dis-
cussed with the detectives a group photo of six young His-
panic males—including Torres and Santillan—that Pomerantz
had provided the LAPD a year earlier when it was investigat-
ing Santillan in connection with another shooting of a Reseda
gang member. The group photo had been taken by a teacher
at a school event called “Melody of Words,” although Detec-
tive Roberts testified at trial that he was unaware of that fact
at the time of Torres’ arrest.

   When Pomerantz originally provided the group photo he
had informed the LAPD that two of the individuals in the
photo (neither of them Torres) were members of the CPA
gang. On September 23, Pomerantz told the detectives that
Torres and Santillan were friends and hung out. In the group
photo, Torres’ right hand is not visible and only part of one
finger of his left hand is visible. Conflicting testimony was
presented at trial as to whether Torres is making a gang sign
with his left hand. However, Detectives Roberts and Park
both testified that, at the time of Torres’ arrest, they were
unaware one way or the other whether Torres was a member
of the CPA gang.

  In all three photos provided by Pomerantz, Torres is wear-
ing a prominent grey metal cross on a chain around his neck.
Pomerantz also told Detective Hickman that Torres “always
wears [a] grey metal cross on a chain around his neck.” Nota-
bly, Hernandez did not say anything about the third male pas-
senger in the car wearing a chain or cross when the detectives
spoke to her on August 25, 2004.
                   TORRES v. CITY OF LOS ANGELES                     11731
   Third, Detective Hickman searched Torres’ name in six dif-
ferent databases: an adult criminal records database, a juve-
nile records database, a Department of Motor Vehicles
records database, the California Criminal History Record Sys-
tem, the Cal-Gangs database, and the gang card file at the
West Valley police station. Detective Hickman found no
matches for Torres.

   Fourth, Detective Hickman used the most recent photo of
Torres she had received from Pomerantz to assemble a photo-
graphic identification array of six individuals called a “six-
pack.”3 Detective Hickman used a computer database to find
photos of five other individuals to place in the six-pack,
which she did by searching for photos based on age and phys-
ical characteristics also applicable to Torres. However, while
Detective Hickman first searched for photos of persons who
were not only young male Hispanics but also “heavy,” that
search did not yield a sufficiently large selection to fill the
six-pack with faces that Detective Hickman considered to be
similar to that of Torres. Accordingly, Detective Hickman
expanded her search to include non-heavy persons, which did
yield a sufficiently large selection. Plaintiffs’ police proce-
dures expert testified at trial that the resulting six-pack was
unduly suggestive because aside from Torres’ photo only one
other photo was of a visibly “chubby” person, thus signifi-
cantly increasing the odds that Hernandez would “identify”
Torres in the lineup.

   Detectives Roberts, Park and Rains then proceeded to the
residence of Hernandez. Detectives Roberts and Park went
inside to show Hernandez the six-pack; Detective Rains
waited outside in his car. Detective Roberts told Hernandez
that he “had possibly identified the 15- to 16-year old chubby
boy” and then read her a standard “photographic show-up
admonition.”
  3
   In the six-pack, the photo of Torres is cropped such that the cross hang-
ing from Torres’ neck chain is not visible.
11732            TORRES v. CITY OF LOS ANGELES
   After Detective Roberts handed Hernandez the six-pack,
Hernandez stared at it—according to Hernandez for between
five and ten minutes—whereupon Detective Roberts asked
her at whom she was staring. Hernandez then indicated that
she was staring at photo #6, the photo of Torres. However,
there was conflicting testimony as to whether Hernandez also
stated that the person in photo #6 was the third male passen-
ger in the car, or, on the contrary, whether she stated that she
did not know whether it was him or not. It is undisputed, how-
ever, that the detectives then asked Hernandez to write down
what she thought, whereupon Hernandez circled the photo of
Torres with a pen and wrote on the six-pack, “I circle the per-
son in #6 because he looks more likely [sic] to the other guy
in the car.” Detective Roberts acknowledged at trial that,
based solely on what Hernandez wrote on the six-pack, he did
not have probable cause to arrest Torres.

   When Detectives Roberts and Park rejoined Detective
Rains outside Hernandez’s home, Detective Roberts told
Rains that Hernandez had identified Torres as the third male
passenger—a statement which Hernandez testified at trial was
false—and said they were going to arrest Torres. Detective
Rains was not shown Hernandez’s written statement on the
six-pack. Detectives Roberts, Park and Rains then went to
Torres’ home. When Torres came outside and the detectives
approached him, Torres did not try to flee. The detectives
engaged in no conversation with Torres but simply arrested
him in his mother’s presence. Detective Park acknowledged
at trial that at the time of Torres’ arrest there was no physical
evidence linking Torres to the shooting.

  Torres was charged with murder and attempted murder
based on his alleged role in the shooting of the two Reseda
gang members. However, on March 4, 2005, after 162 days
of incarceration, Torres was released when the district attor-
ney dismissed the charges against him.

  Torres and his mother subsequently filed suit, claiming
deprivation of Torres’ Fourth Amendment rights, in violation
                   TORRES v. CITY OF LOS ANGELES                   11733
of 42 U.S.C. § 1983, as well as false arrest and negligent
infliction of emotional distress, in violation of California law.
Defendants moved for partial summary judgment on Plain-
tiffs’ claims against the City of Los Angeles and the LAPD
on the ground that Plaintiffs could not prove liability under
Monell v. New York City Department of Social Services, 436
U.S. 658 (1978). In their motion, Defendants stated that
“[b]ecause triable issues of material fact exist regarding prob-
able cause for Plaintiff’s arrest, Defendants move for partial
summary judgment on Monell liability only.” The district
court granted the motion, a ruling Plaintiffs do not appeal.

   On the eve of trial against the remaining Defendants, the
district court denied two of Plaintiffs’ motions in limine: a
motion for an order barring Defendants’ expert witnesses
Detective Jack Giroud and Officer Norm Peters from testify-
ing on the ground that they had failed to provide written
expert reports as required by Federal Rule of Civil Procedure
26(a)(2)(B); and a motion for an order barring the investigat-
ing detectives and all defense experts from testifying that, in
their opinion, probable cause existed to arrest Torres.

   After all of the parties had presented their evidence to the
jury, Defendants orally moved for judgment as a matter of
law, pursuant to Federal Rule of Civil Procedure 50(a), as to
all of Plaintiffs’ claims. The district court granted the motion
and dismissed Plaintiffs’ case. In its written order, the district
court concluded that Detectives Hickman and Rains had not
been involved in Torres’ arrest and therefore could not be lia-
ble. The court further concluded that Detectives Park and
Roberts had probable cause to arrest Torres and that, accord-
ingly, Plaintiffs’ § 1983 claim and state law claims should be
dismissed.4 Finally, the court concluded that even if Detec-
tives Park and Roberts did not have probable cause to arrest
  4
    The district court dismissed Plaintiffs’ state law claim for negligent
infliction of emotional distress because it was predicated on their claims
for violation of civil rights and false arrest.
11734               TORRES v. CITY OF LOS ANGELES
Torres, they were protected from Plaintiffs’ § 1983 claim by
qualified immunity.5

                                     II.

   We review de novo the district court’s order granting
Defendants’ motion for judgment as a matter of law under
Rule 50(a). See Santos v. Gates, 287 F.3d 846, 851 (9th Cir.
2002). “Judgment as a matter of law is appropriate when the
evidence presented at trial permits only one reasonable con-
clusion.” Id. In other words, “[a] motion for a judgment as a
matter of law is properly granted only if no reasonable juror
could find in the non-moving party’s favor.” El-Hakem v. BJY
Inc., 415 F.3d 1068, 1072 (9th Cir. 2005). “The evidence
must be viewed in the light most favorable to the nonmoving
party, and all reasonable inferences must be drawn in favor of
that party.” LaLonde v. County of Riverside, 204 F.3d 947,
959 (9th Cir. 2000). “If conflicting inferences may be drawn
from the facts, the case must go to the jury.” Id.

   We also review de novo the district court’s finding of prob-
able cause, Rosenbaum v. City and County of San Francisco,
484 F.3d 1142, 1161 n.14 (9th Cir. 2007), as well as its grant
of qualified immunity, Aguilera v. Baca, 510 F.3d 1161, 1167
(9th Cir. 2007). We review for an abuse of discretion the dis-
trict court’s evidentiary rulings. Janes v. Wal-Mart Stores,
Inc., 279 F.3d 883, 886 (9th Cir. 2002).
  5
    In its written order, the district court made findings of fact and reached
conclusions of law as “required by Rule 52 of the Federal Rules of Civil
Procedure.” This was error because the case was being tried to a jury. See
Fed. R. Civ. P. 52(a)(1) (“In an action tried on the facts without a jury or
with an advisory jury, the court must find the facts specially and state its
conclusions of law separately.” (emphasis added)). Instead, the court
should have determined only whether “a reasonable jury would not have
a legally sufficient evidentiary basis” to find for the non-moving party. See
Fed. R. Civ. P. 50(a)(1).
                TORRES v. CITY OF LOS ANGELES             11735
                              III.

                              A.

   [1] We affirm the district court’s dismissal of Plaintiffs’
case against Detective Hickman. The evidence is undisputed
that Detective Hickman was not present when Torres was
arrested, and there is no evidence that Detective Hickman
instructed the other detectives to arrest Torres or that any of
those detectives consulted with her before making the arrest.
Thus, there is no evidence of “integral participation” by
Detective Hickman in the alleged constitutional violation.
Chuman v. Wright, 76 F.3d 292, 294-95 (9th Cir. 1996); see
Blankenhorn v. City of Orange, 485 F.3d 463, 481 n.12 (9th
Cir. 2007) (explaining that integral participation requires
“some fundamental involvement in the conduct that allegedly
caused the violation” and affirming summary judgment in
favor of officer who arrived on the scene after the allegedly
unconstitutional arrest and officer who provided only crowd
control (citing Boyd v. Benton County, 374 F.3d 773, 780 (9th
Cir. 2004)); Motley v. Parks, 432 F.3d 1072, 1082 (9th Cir.
2005) (en banc) (affirming grant of summary judgment in
favor of government agent who did not participate in the
allegedly unconstitutional search).

   [2] Moreover, although Detective Park testified that Detec-
tive Hickman, together with Detective Roberts, was in charge
of the investigation of the shooting, there is no evidence that
Detective Hickman acted as a supervisor that would impose
supervisor liability. See Motley, 432 F.3d at 1081 (“A supervi-
sor can be liable under § 1983 if he ‘set[s] in motion a series
of acts by others . . . , which he knew or reasonably should
have known, would cause others to inflict the constitutional
injury.’ ” (modifications in original) (quoting Larez v. City of
Los Angeles, 946 F.2d 630, 646 (9th Cir.1991)).
11736               TORRES v. CITY OF LOS ANGELES
                                      B.

  Plaintiffs argue that the district court erred in concluding,
as a matter of law, that Detectives Roberts, Park and Rains
had probable cause to arrest Torres.6

   [3] “Probable cause to arrest exists when officers have
knowledge or reasonably trustworthy information sufficient to
lead a person of reasonable caution to believe that an offense
has been or is being committed by the person being arrested.”
United States v. Lopez, 482 F.3d 1067, 1072 (9th Cir. 2007)
(citing Beck v. Ohio, 379 U.S. 89, 91 (1964)). “While conclu-
sive evidence of guilt is of course not necessary under this
standard to establish probable cause, ‘[m]ere suspicion, com-
mon rumor, or even strong reason to suspect are not
enough.’ ” Id. (quoting McKenzie v. Lamb, 738 F.2d 1005,
1008 (9th Cir. 1984)). Under the collective knowledge doc-
trine, in determining whether probable cause exists for arrest,
we look to “the collective knowledge of all the officers
involved in the criminal investigation[.]” United States v.
Ramirez, 473 F.3d 1026, 1032 (9th Cir. 2007) (internal quota-
tion marks omitted).

  [4] As the definition of probable cause indicates, the proper
inquiry is whether the detectives had probable cause to
believe that Torres had committed a crime, not merely that
Torres was the third male passenger in the car.7 While proba-
  6
     While the district court dismissed Plaintiffs’ case against Detective
Rains on the ground that “there was no evidence showing that Rains was
involved in the arrest of Plaintiff” because “[a]ccording to the evidence,
Rains was only acting as backup during Plaintiff’s arrest and did not per-
sonally assist in or direct the arrest of Plaintiff,” we disagree with this con-
clusion in light of Rains’ own testimony that “I was involved in the
arrest.”
   7
     Defendants assert that Plaintiffs’ case “has always rested on whether
there was probable cause to believe that [Torres] was the third suspect in
[Hernandez’s] vehicle,” not on whether there was probable cause to
believe that Torres was guilty of murder. However, we consider only the
                    TORRES v. CITY OF LOS ANGELES                    11737
ble cause supports an arrest so long as the arresting officers
had probable cause to arrest the suspect for any criminal
offense, regardless of their stated reason for the arrest, see
Devenpeck v. Alford, 543 U.S. 146, 153-55 (2004); see also
Virginia v. Moore, 128 S. Ct. 1598, 1604 (2008), an arrest is
still unlawful unless probable cause existed under a specific
criminal statute, see Devenpeck, 543 U.S. at 156. Defendants
do not contend that there was probable cause to believe that
Torres had committed any offense besides murder and
attempted murder. In California, both offenses require an
unlawful killing with malice aforethought, see Cal. Penal
Code §§ 187, 664, although malice is implied “when a killing
results from an intentional act, the natural consequences of
which are dangerous to human life, and the act is deliberately
performed with knowledge of the danger to, and with con-
scious disregard for, human life[,]” People v. Cook, 139 P.3d
492, 515 (Cal. 2006) (citation omitted). Therefore, the ques-
tion is whether the detectives had probable cause to believe
that Torres had acted in concert with the shooter, Castaneda,
with conscious disregard for human life.8

latter question because an arrest is lawful under the Fourth Amendment
only if it is accompanied by probable cause to believe that the arrestee has
committed, or is committing, an offense. See, e.g., Lopez, 482 F.3d at
1072. Mere presence in a vehicle in which a crime is being committed is
not an offense. See United States v. Herrera-Gonzalez, 263 F.3d 1092,
1097-98 (9th Cir. 2001) (“Sometimes youthful inexperience and lack of
common sense, impecuniousness, or personal relationships may bring the
innocent into continuing proximity with the guilty, but our line of ‘mere
presence’ cases requires acquittal in the absence of evidence of intentional
participation.”).
   8
     Defendants “presume” that Torres was arrested and charged with mur-
der on a provocative act murder theory, a theory that can be applied in
“situations in which criminal defendants neither kill nor intend to kill, but
cause a third party to kill in response to their life-threatening provocative
acts.” People v. Cervantes, 29 P.3d 225, 230 (Cal. 2001). However, to the
extent Defendants suggest that Torres’ alleged flashing of gang signs and
shouting of challenges, alone, could constitute the intentional act neces-
sary for murder liability, we disagree. “To satisfy the ‘actus reus’ element
11738              TORRES v. CITY OF LOS ANGELES
   In reviewing the grant of a motion for judgment as a matter
of law, we must determine whether a reasonable jury could
have concluded that the detectives lacked probable cause to
arrest Torres. See, e.g., Monroe v. City of Phoenix, Arizona,
248 F.3d 851, 861-62 (9th Cir. 2001) (affirming denial of
Rule 50(a) motion in excessive force case because “[a] rea-
sonable jury could conclude that [the defendant officer] had
probable cause to believe that [the plaintiff] posed a threat of
serious physical harm”), overruled on other grounds as rec-
ognized in Acosta v. Hill, 504 F.3d 1323, 1324 (9th Cir.
2007). Defendants concede that, because we must view the
evidence in the light most favorable to Plaintiffs and draw all
reasonable inferences in their favor, we must assume the fol-
lowing: that school police officer Steinberg did not tell Offi-
cer Lamar or Detective Hickman that Torres had “recently
been jumped into the CPA gang”; that in the group photo Tor-
res is not visibly making a gang sign (or that it was unreason-
able for the detectives to conclude that he is); and that
Hernandez did not positively identify Torres as the third male
passenger in the car.

   We conclude that, based on the information in the detec-
tives’ possession at the time of the arrest, a reasonable jury
could have found that the detectives lacked probable cause to
believe that Torres had been the third male passenger in the
car and had acted in concert with the shooter with conscious
disregard for human life.

of [provocative act murder] the defendant or one of his confederates must
commit an act which provokes a third party into firing the fatal shot.” In
re Aurelio R., 212 Cal. Rptr. 868, 870 (Cal. Ct. App. 1985). “[N]o criminal
liability attaches to an initial remote actor for an unlawful killing that
results from an independent intervening cause (i.e., a superseding cause).”
Cervantes, 29 P.3d at 231. Here, the evidence shows that Castaneda fired
the shots not because he was provoked by his fellow passenger’s flashing
of gang signs and shouting of challenges, but rather by the fact that the
Reseda gang members chased the car driven by Santillan.
                TORRES v. CITY OF LOS ANGELES            11739
   [5] First, Hernandez’s general description of the third male
passenger is not sufficient to create probable cause. “ ‘Under
the law of this Circuit, mere resemblance to a general descrip-
tion is not enough to establish probable cause.’ ” Lopez, 482
F.3d at 1073 (quoting Grant v. City of Long Beach, 315 F.3d
1081, 1088 (9th Cir. 2002)). For example, in United States v.
Ricardo D., we held that the fact that the defendant matched
descriptions of the crime suspect as a “young, thin man, not
too tall” and a “young, Mexican male” were insufficient to
create probable cause. 912 F.2d 337, 342 (9th Cir. 1990).
Here, Hernandez’s description of the third male passenger
was slightly more detailed than the description in Ricardo D.
but, at the same time, did not match Torres insofar as Her-
nandez described the third male passenger as having some
hair. Moreover, the fact that Hernandez did not mention a
chain or cross around the passenger’s neck casts further doubt
on whether Torres matched Hernandez’s general description.
Accordingly, Hernandez’s description alone was clearly
insufficient to create probable cause as a matter of law.

   [6] Second, a reasonable jury could have found that Her-
nandez’s “identification” of Torres in the six-pack did not
create probable cause because the six-pack was suggestive
and the “identification” was not sufficiently reliable. See
Grant, 315 F.3d at 1086-88 (holding that two identifications
did not create probable cause as a matter of law because six-
pack was arguably suggestive and identifications lacked suffi-
cient indicia of reliability).

   The Supreme Court has cautioned that “[a] major factor
contributing to the high incidence of miscarriage of justice
from mistaken identification has been the degree of sugges-
tion inherent in the manner in which the prosecution presents
the suspect to witnesses for pretrial identification.” United
States v. Wade, 388 U.S. 218, 228 (1967). Here, only one
other photo in the six-pack besides the photo of Torres was
of a visibly overweight individual and thus of a person who
fit Hernandez’s general description. In addition, Detective
11740           TORRES v. CITY OF LOS ANGELES
Roberts told Hernandez, before handing her the six-pack, that
the detectives had “possibly identified the 15 to 16 year-old
chubby boy.” According to Plaintiffs’ expert, that statement
was “absolutely forbidden” and “contaminate[d] the identifi-
cation,” presumably because it informed Hernandez that the
detectives’ suspect was among the photos in the six-pack and
thus could have pressured her to make an identification.
Based on these facts, a reasonable jury could have found the
six-pack to be impermissibly suggestive.

   Although a suggestive photo array “may still serve as a
basis for probable cause if sufficient indicia of reliability are
present,” Grant, 315 F.3d at 1087 (citing United States v.
Hanigan, 681 F.2d 1127, 1131 (9th Cir. 1982)), here a reason-
able jury could have found that no sufficient indicia of reli-
ability were present. “Indicia of reliability include: 1) the
opportunity to view the criminal at the time of the crime; 2)
the degree of attention paid to the criminal; 3) the accuracy
of the prior descriptions of the criminal; 4) the level of cer-
tainty demonstrated at the time of the confrontation; and
5) [ ] the length of time between the crime and the confronta-
tion.” Id. (citing Gray v. Klauser, 282 F.3d 633, 639 (9th Cir.
2002)). While Hernandez spent several hours in the car with
the third male passenger, she had never seen him before and
did not pay attention to him. In addition, as previously dis-
cussed, Hernandez gave only a general description of the third
male passenger, which did not match Torres in two important
respects (head of hair and no mention of prominent cross).
Further, Hernandez was not shown the six-pack until six
weeks after the shooting. When she was handed the six-pack,
she stared at it in silence for between five and ten minutes and
then, when asked at whom she was staring, made only a com-
parative identification: she stated that Torres looked more like
the third male passenger than the other persons depicted in the
six-pack (only one of whom was visibly overweight), but that
she was not sure whether or not it actually was him. Thus, a
reasonable jury could have concluded that Hernandez’s iden-
tification lacked sufficient indicia of reliability and thus did
                TORRES v. CITY OF LOS ANGELES              11741
not provide the detectives with probable cause. Although
Detective Rains had been told that Hernandez had positively
identified Torres, we nevertheless conclude that the reliability
of the identification was sufficiently questionable for other
reasons to allow a reasonable jury to conclude that Rains, too,
lacked probable cause.

   [7] While the detectives also had the additional information
that Torres was friends with Santillan, hung out with gang
members, and had recently begun “dressing down as a gang-
ster,” they had no information that Torres was actually a
member of the CPA gang (or any other gang), and Torres’
name did not come up in any of the six criminal databases
searched by Detective Hickman. Moreover, although finger-
prints of Santillan were found in the car, there was no physi-
cal evidence linking Torres to the vehicle. In addition, the fact
that Torres made no attempt to flee when the detectives came
to arrest him, while by no means dispositive, further indicates
that reasonable minds could disagree about the existence of
probable cause. See Ricardo D., 912 F.2d at 342.

   [8] Finally, the detectives lacked evidence that the third
male passenger had acted in concert with Castaneda and had
the requisite mental state to be guilty of murder and attempted
murder. There is no evidence that the third male passenger
helped decide or make plans to challenge or shoot at rival
gang members; that he knew that Castaneda had a gun; or that
he assisted Castaneda in firing the shots. Thus, aside from the
evidence that the third male passenger had flashed gang signs
and shouted challenges, there was no evidence that the third
male passenger had acted in concert with Castaneda and had
done so with a conscious disregard for human life. This dearth
of evidence as to the third male passenger’s culpability further
widens the gap between mere suspicion and probable cause to
believe that Torres had committed a crime.

  [9] Accordingly, we conclude that a reasonable jury could
have found that Detectives Roberts, Park and Rains lacked
11742            TORRES v. CITY OF LOS ANGELES
probable cause to believe that Torres had committed a crime.
The district court therefore erred in finding probable cause as
a matter of law.

                               C.

   We next consider whether Detectives Roberts, Park and
Rains were nevertheless protected by qualified immunity.
When a police officer asserts qualified immunity, we apply a
two-part analysis under Saucier v. Katz, 533 U.S. 194 (2001).
The first question is whether the facts, when taken in the light
most favorable to Plaintiffs, show that Defendants’ conduct
violated a constitutional right. Id. at 201. The second question
is whether the constitutional right at issue is “clearly estab-
lished.” Id. at 202.

   Initially, Defendants argue that the qualified immunity
issue is one for the court, not the jury, to decide. The implica-
tion of their argument is that we must decide as a matter of
law whether or not Defendants are protected by qualified
immunity, not whether a reasonable jury could have found
that they are not protected by qualified immunity. We reject
Defendants’ argument in light of the procedural posture of
this case and the existence of material issues of disputed fact.

   [10] Plaintiffs here appeal the grant of a Rule 50(a) motion
made after completion of the trial but before a jury verdict.
While the Supreme Court has encouraged resolution of the
qualified immunity issue early on in the lawsuit, such as at the
summary judgment stage, see Saucier, 533 U.S. at 200
(“Where the defendant seeks qualified immunity, a ruling on
that issue should be made early in the proceedings so that the
costs and expenses of trial are avoided where the defense is
dispositive.”), Defendants chose not to move for summary
judgment on qualified immunity grounds, acknowledging that
“triable issues of material fact exist regarding probable cause
for Plaintiff’s arrest.” Thus, the case proceeded to trial before
a jury. While at the summary judgment stage the qualified
                   TORRES v. CITY OF LOS ANGELES                     11743
immunity issue is necessarily decided by the court if it turns
on issues of law, we have approved the submission of the
qualified immunity issue to the jury where genuine issues of
material fact exist. See, e.g., Grant, 315 F.3d at 1090 (holding
that “the district court properly submitted the issue of quali-
fied immunity to the jury and entered judgment upon its ver-
dict” because defendants were not entitled to qualified
immunity as a matter of law); LaLonde, 204 F.3d at 953 (“If
. . . there is a material dispute as to the facts regarding what
the officer or the plaintiff actually did, the case must proceed
to trial, before a jury if requested.” (citing Act Up!/Portland
v. Bagley, 988 F.2d 868, 873 (9th Cir. 1993)); Thompson v.
Mahre, 110 F.3d 716, 719 (9th Cir. 1997) (“[W]here there is
a genuine issue of fact on a substantive issue of qualified
immunity, ordinarily the controlling principles of summary
judgment and, if there is a jury demand and a material issue
of fact, the Seventh Amendment, require submission to a
jury.”); see also Sloman v. Tadlock, 21 F.3d 1462, 1468 (9th
Cir. 1994) (explaining that the reasons for the existence of the
qualified immunity doctrine “do not . . . suggest that a judicial
determination at [the trial] stage is necessarily better than a
jury verdict” (emphasis in original)).9 Indeed, we have
explained that “sending the factual issues to the jury but
reserving to the judge the ultimate ‘reasonable officer’ deter-
mination leads to serious logistical difficulties.” Sloman, 21
F.3d at 1468.

   [11] Defendants contend that our decision in Peng v. Mei
Chin Penghu, 335 F.3d 970 (9th Cir. 2003), supports their
contention that a court, not a jury, must decide the qualified
immunity issue. We disagree. In Peng, the district court had
determined at the summary judgment stage that the defendant
officer was entitled to qualified immunity. Id. at 972-73. On
  9
    As we noted in Sloman, when a case proceeds to trial “qualified immu-
nity can no longer rightly be called an ‘immunity from suit’ (since the suit
has already proceeded to its conclusion); rather, it is now effectively a
defense.” 21 F.3d at 1468 n.6.
11744           TORRES v. CITY OF LOS ANGELES
appeal, Peng argued, first, that the existence of disputes of
fact precluded the district court from granting summary judg-
ment on the issue of qualified immunity, and, second, that
because more than one reasonable inference could be drawn
from the undisputed facts regarding the existence of probable
cause, the question of probable cause was one for the jury and
not the court. Id. at 978-79. Rejecting both arguments, this
court held that the factual disputes were not material to the
qualified immunity issue, id., and that, “where the material,
historical facts are not in dispute, and the only disputes
involve what inferences properly may be drawn from those
historical facts, it is appropriate for this court to decide
whether probable cause existed at the time [the officer]
arrested Peng,” id. at 979-80 (emphasis added).

   [12] However, in this case the material, historical facts are
in dispute. Disputes of fact exist as to whether Hernandez
positively identified Torres, whether school police officer
Steinberg told Officer Lamar and/or Detective Hickman that
Torres had “recently been jumped into the CPA gang,” and
whether it was reasonable for the detectives to believe that in
the group photo Torres was making a gang sign despite the
fact that only one of Torres’ fingers is visible in the photo.
These disputes of fact are material because they go to what
the detectives knew at the time they arrested Torres and,
accordingly, to whether they had probable cause, and reason-
ably believed they had probable cause, to do so. Accordingly,
Peng does not help Defendants.

  With respect to the first Saucier question, we have already
determined that a reasonable jury could find that Defendants
violated Torres’ constitutional right to be free from arrest
without probable cause. See Grant, 315 F.3d at 1089 (“Courts
have long held that the Fourth Amendment requires probable
cause before an officer may arrest an individual.” (citing
Beck, 379 U.S. at 91)). In answering the second question,
whether the constitutional right was clearly established, we do
not consider the right as a “general proposition.” Saucier, 533
                 TORRES v. CITY OF LOS ANGELES             11745
U.S. at 201. Rather, “[t]he relevant, dispositive inquiry . . . is
whether it would be clear to a reasonable officer that his con-
duct was unlawful in the situation he confronted.” Id. at 202.
“Qualified immunity is an objective inquiry—whether the
officers subjectively believed that they had probable cause to
arrest [Torres] is irrelevant.” Grant, 315 F.3d at 1089 (citing
Anderson v. Creighton, 483 U.S. 635, 641 (1987)).

   [13] We conclude that a jury could have found that it would
be clear to a reasonable officer that arresting Torres was
unlawful for lack of probable cause. In light of the arguably
suggestive six-pack, Hernandez’s merely comparative identi-
fication six weeks after the shooting, the lack of direct evi-
dence that Torres was a member of a gang (let alone the CPA
gang), the lack of physical evidence tying Torres to the shoot-
ing, the fact that Torres did not attempt to flee when the
detectives approached him, and the lack of evidence that the
third male passenger acted in concert with Castaneda with
conscious disregard for human life, “[a] material issue of fact
existed as to whether a reasonable officer would have relied
on [the information in the detectives’ possession] without fur-
ther verification.” Grant, 315 F.3d at 1090. Accordingly,
“there was enough evidence for a reasonable jury to conclude
that reasonable officers would not have acted as [Detectives
Roberts and Park] did in arresting [Torres].” Id. We therefore
conclude that Detectives Roberts and Park were not entitled
to qualified immunity as a matter of law.

   However, we reach a different conclusion as to Detective
Rains. Because Detective Roberts told Rains that Hernandez
had identified Torres and because he did not show Rains Her-
nandez’s written statement on the six-pack, Rains believed
that Hernandez had positively identified Torres.

   While “[a]ll officers . . . have an ongoing duty to make
appropriate inquiries regarding the facts received or to further
investigate if sufficient details are relayed,” Motley, 432 F.3d
at 1081 (citation omitted), we have explained that “[w]here an
11746           TORRES v. CITY OF LOS ANGELES
officer has an objectively reasonable, good-faith belief that he
is acting pursuant to proper authority, he cannot be held liable
if the information supplied by other officers turns out to be
erroneous.” id. at 1082 (citing United States v. Hensley, 469
U.S. 221, 232 (1985)). “The lynchpin is whether the officer’s
reliance on the information was objectively reasonable.” Id.

   [14] In light of what Detective Roberts told Detective Rains
after showing the six-pack to Hernandez, and in light of the
undisputed fact that, of the four detectives, Detective Rains
was the least involved in the investigation, we conclude as a
matter of law that Detectives Rains reasonably relied on the
(allegedly false) statement by Detective Roberts that Her-
nandez had identified Torres. Based on this conclusion, we
further conclude as a matter of law that a reasonable officer
in Rains’ position would have believed he had probable cause
to arrest Torres. Accordingly, Detective Rains was entitled to
qualified immunity as a matter of law.

                              D.

   We deal with the following evidentiary issues to guide the
district court on remand. Plaintiffs contend that the district
court abused its discretion in denying their motion in limine
seeking to bar the testimony of Defendants’ expert witnesses
Detective Jack Giroud and Officer Norm Peters on the ground
that Defendants failed to provide Plaintiffs written expert
reports for those witness pursuant to Federal Rule of Civil
Procedure 26(a)(2)(B).

  Rule 26(a)(2)(B) provides that, “[u]nless stipulated or
ordered by the court, [the disclosure of the identity of wit-
nesses pursuant to Rule 26(a)(2)(A)] must be accompanied by
a written report—prepared and signed by the witness—if the
witness is one retained or specially employed to provide
expert testimony in the case or one whose duties as the party’s
employee regularly involve giving expert testimony.” Fed. R.
Civ. P. 26(a)(2)(B). We have explained that “Rule 37(c)(1)
                       TORRES v. CITY OF LOS ANGELES                      11747
gives teeth to [this requirement] by forbidding the use at trial
of any information required to be disclosed by Rule 26(a) that
is not properly disclosed.” Yeti by Molly, Ltd. v. Deckers Out-
door Corp., 259 F.3d 1101, 1106 (9th Cir. 2001).10

   [15] We agree with Plaintiffs that Officer Peters should not
have been permitted to testify without providing a written
expert report. Peters, whom Defendants called as a “gang spe-
cialist,” testified that he was regularly employed to give
expert opinions in court about gangs. Accordingly, Peters
falls squarely in the category of witnesses to which Rule
26(a)(2)(B) applies.

   We reject Defendants’ argument that Plaintiffs were
required, but failed, to articulate how they would be preju-
diced if they were not provided an expert witness report.
Defendants advance two bases for their argument. First, they
contend that the purpose of an expert report is “the elimina-
tion of unfair surprise to the opposing party and the conserva-
tion of resources,” Sylla-Sawdon v. Uniroyal Goodrich Tire
Co., 47 F.3d 277, 284 (8th Cir. 1995), and that because “Rule
26 focuses not on the status of the witness, but rather on the
substance of the testimony,” Patel v. Gayes, 984 F.2d 214,
218 (7th Cir. 1993) (superseded on other grounds by amend-
ment to the Federal Rules of Civil Procedure, as recognized
in Musser v. Gentiva Health Servs., 356 F.3d 751, 757 n.2
(7th Cir. 2004)), Plaintiffs must articulate how the failure to
provide them with an expert report led to surprise at trial. This
contention fails. In Patel, the Seventh Circuit focused on the
substance of the testimony rather than the status of the witness
  10
    Rule 37(c)(1) provides in relevant part:
       If a party fails to provide information or identify a witness as
       required by Rule 26(a) or (e), the party is not allowed to use that
       information or witness to supply evidence on a motion, at a hear-
       ing, or at trial, unless the failure was substantially justified or is
       harmless.
Fed. R. Civ. P. 37(c)(1).
11748           TORRES v. CITY OF LOS ANGELES
not to determine whether the party moving under Rule 26
would be prejudiced by the lack of an expert report but only
to determine whether the witnesses in question were experts
for purposes of Rule 26(a)(2)(B) or instead fell under the
“treating physician” exception and therefore were not
required to prepare an expert report in the first place. See
Patel, 984 F.2d at 218. Thus, Patel does not support Defen-
dants’ argument.

   The second basis for Defendants’ argument is that Rule
37(c)(1) provides that a party who fails to comply with Rule
26(a) may not use the witness in question to supply evidence
at trial “unless the failure was substantially justified or is
harmless.” Fed. R. Civ. P. 37(c)(1) (emphasis added). Based
on this Rule, Defendants contend that Officer Peters could
testify without providing an expert report because Plaintiffs
failed to articulate how they would be prejudiced without
such a report. This contention also fails. Rule 37(c)(1) pro-
vides a sanction for failure to comply with the disclosure
requirements of Rule 26(a). See Fed R. Civ. P. 37 advisory
committee’s note, 1993 Amendments. In determining whether
this sanction should be imposed, the burden is on the party
facing the sanction—i.e., Defendants—to demonstrate that the
failure to comply with Rule 26(a) is substantially justified or
harmless. See Yeti by Molly, Ltd., 259 F.3d at 1107 (“Implicit
in Rule 37(c)(1) is that the burden is on the party facing sanc-
tions to prove harmlessness.”). Thus, Plaintiffs were not
required to articulate how they would be prejudiced by Defen-
dants’ failure to provide an expert report. Because the district
court denied Plaintiffs’ motion in limine without explanation,
there is no basis for us to conclude that the failure to provide
an expert report was substantially justified or harmless for
purposes of Rule 37(c)(1).

   [16] Therefore, we conclude that the district court abused
its discretion in denying Plaintiffs’ in limine motion. We
instruct the court, on remand and upon proper motion by
Plaintiffs, to require that Defendants, pursuant to Rule
                   TORRES v. CITY OF LOS ANGELES                     11749
26(a)(2)(B), provide Plaintiffs with an expert report prepared
by Officer Peters if they wish to call him as an expert witness.

   However, we do not reach the same conclusion with respect
to Detective Giroud. While Defendants concede that Detec-
tive Giroud was an expert witness, not all expert witnesses
must provide an expert report. By exclusion, Rule 26(a)(2)(B)
contemplates that individuals who are employed by a party
and whose duties do not regularly involve giving expert testi-
mony need not provide an expert report. See, e.g., Watson v.
United States, 485 F.3d 1100, 1107 (10th Cir. 2007); Bank of
China, New York Branch v. NBM LLC, 359 F.3d 171, 182
n.13 (2d Cir. 2004). We have found no evidence in the record
that the duties of Detective Giroud, who was employed by the
LAPD, regularly involved giving expert testimony. Accord-
ingly, on this record, we cannot determine whether Rule
26(a)(2)(B) applied to him. We therefore leave it to the dis-
trict court, on remand, to determine whether Rule 26(a)(2)(B)
requires Defendants to provide Plaintiffs with an expert report
prepared by Detective Giroud.11

                                   IV.

  We affirm the district court’s dismissal of Plaintiffs’ case
against Detective Hickman and of Plaintiffs § 1983 claim
  11
     Keeping in mind that the inquiry is whether objectively the officers
reasonably believed they had probable cause, we also agree with Plaintiffs
that the district court abused its discretion in denying their motion in
limine seeking to bar Defendants’ witnesses from testify as to their own
opinion about whether there was probable cause to arrest Torres. See Stu-
art v. United States, 23 F.3d 1483, 1487 (9th Cir. 1994) (upholding district
court’s ruling that barred plaintiff’s expert from opining as to whether
probable cause existed on the ground that the jury was more suited than
the expert to answer the question); see also Peterson v. City of Plymouth,
60 F.3d 469, 476 n.10 (8th Cir. 1995); Estes v. Moore, 993 F.2d 161, 163
(8th Cir. 1998). Defendants did not address this issue in their brief and
effectively conceded the issue at oral argument. Accordingly, we instruct
the district court, on remand, to bar Defendants’ witnesses from testifying
as to their opinion that they had probable cause to arrest Torres.
11750              TORRES v. CITY OF LOS ANGELES
against Detective Rains.12 We reverse the grant of judgment
as a matter of law as to Detectives Roberts and Park. We
reverse in part the denial of Plaintiffs’ in limine motions.

  [17] Plaintiffs are awarded costs on appeal.

 AFFIRMED in part, REVERSED in part, and
REMANDED.




  12
    Because we conclude that a reasonable jury could have found that all
Defendants, including Detective Rains, lacked probable cause to arrest
Torres, Plaintiffs’ California law claims against Detective Rains, which
are not affected by our conclusion that Rains is protected by qualified
immunity, should not have been dismissed. See Blankenhorn, 485 F.3d at
489 (Berzon, J., concurring in part and dissenting in part); Brown v. Li,
308 F.3d 939, 955 (9th Cir. 2002).
