                FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


UNITED STATES OF AMERICA,             No. 08-50479
                Plaintiff-Appellee,
                                         D.C. No.
                v.                    5:05-cr-00069-
                                          VAP-3
OSCAR RODRIGUEZ, AKA Lonely,
            Defendant-Appellant.



UNITED STATES OF AMERICA,             No. 08-50483
                Plaintiff-Appellee,
                                         D.C. No.
                v.                    5:05-cr-00069-
                                          VAP-2
JOSE MURILLO, AKA Yogi,
              Defendant-Appellant.



UNITED STATES OF AMERICA,             No. 08-50485
                Plaintiff-Appellee,
                                         D.C. No.
                v.                    5:05-cr-00069-
                                          VAP-4
ALEJANDRO MUJICA, AKA Slow,
            Defendant-Appellant.
2                UNITED STATES V. RODRIGUEZ

 UNITED STATES OF AMERICA,                         No. 12-50121
                 Plaintiff-Appellee,
                                                      D.C. No.
                      v.                           5:05-cr-00069-
                                                       VAP-3
 OSCAR RODRIGUEZ, AKA Lonely,
             Defendant-Appellant.


 UNITED STATES OF AMERICA,                         No. 12-50132
                 Plaintiff-Appellee,
                                                      D.C. No.
                      v.                           5:05-cr-00069-
                                                       VAP-2
 JOSE MURILLO, AKA Yogi,
               Defendant-Appellant.                   OPINION

        Appeal from the United States District Court
            for the Central District of California
        Virginia A. Phillips, District Judge, Presiding

                    Argued and Submitted
            August 28, 2013—Pasadena, California

                       Filed June 19, 2014

    Before: Ronald M. Gould and Johnnie B. Rawlinson,
    Circuit Judges, and Ivan L.R. Lemelle, District Judge.*

                  Opinion by Judge Rawlinson


 *
   The Honorable Ivan L.R. Lemelle, U.S. District Judge for the Eastern
District of Louisiana, sitting by designation.
                 UNITED STATES V. RODRIGUEZ                            3

                           SUMMARY**


                           Criminal Law

   The panel affirmed three defendants’ convictions for
conspiracy to commit murder and first degree murder
stemming from the stabbing of a prison inmate, Peter
Scopazzi.

    The panel held that the district court’s exclusion of
evidence concerning medical negligence and Scopazzi’s
removal of his breathing tube does not warrant reversal of the
convictions, where the defendants failed to demonstrate that
any medical negligence related to Scopazzi’s multiple stab
wounds and his removal of his breathing tube were the sole
causes of his death or were so extraordinary and
unforeseeable as to absolve the defendants of liability for
their vicious assault.

    The panel held that the district court did not abuse its
discretion in admitting evidence of the defendants’
connections to the Mexican Mafia to demonstrate their
motive for murdering Scopazzi. The panel also held that
expert testimony concerning the connections between the
Sureños and the Mexican Mafia within the prison gang
hierarchy and photographs of the defendants with Mexican
Mafia members did not render their trial unfair because the
district court properly minimized any prejudice stemming
from the evidence and the trial was replete with admissible
evidence regarding the defendants’ gang affiliations.

  **
     This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
4              UNITED STATES V. RODRIGUEZ

    The panel held that the defendants failed to demonstrate
under Brady, Mooney, or Napue that a new trial was
warranted based on the government’s failure to disclose
immaterial information regarding a government witness’
sentence reduction and his cooperation in a DEA
investigation.


                        COUNSEL

Verna Wefald (argued), Pasadena, California, for Defendant-
Appellant Oscar Rodriguez.

Michael J. Treman, Santa Barbara, California, for Defendant-
Appellant Jose Murillo.

Ethan A. Balogh (argued) and Jay A. Nelson, Coleman &
Balogh LLP, San Francisco, California, for Defendant-
Appellant Alejandro Mujica.

André Birotte, Jr., United States Attorney, Robert E. Dugdale,
Chief Assistant United States Attorney, Antoine F. Raphael
(argued), Assistant United States Attorney, Riverside,
California, for Plaintiff-Appellee United States.


                         OPINION

RAWLINSON, Circuit Judge:

   Appellants Oscar Rodriguez (Rodriguez), Jose Murillo
(Murillo), and Alejandro Mujica (Mujica) challenge their
convictions for conspiracy to commit murder and first degree
murder stemming from the stabbing of a prison inmate, Peter
               UNITED STATES V. RODRIGUEZ                     5

Scopazzi (Scopazzi) at the United States Penitentiary at
Victorville, California. Appellants contend that the district
court abused its discretion in excluding evidence that medical
negligence and Scopazzi’s removal of his breathing tube
during his hospitalization may have been the proximate cause
of Scopazzi’s death. Appellants also argue that the district
court abused its discretion in admitting expert testimony
concerning the relationship between two prison gangs—the
Sureños and the Mexican Mafia—because Appellants were
not members of the Mexican Mafia.

     Additionally, Appellants maintain that a new trial was
warranted because the government failed to disclose, as
required by Brady v. Maryland, 373 U.S. 83 (1963) and
Giglio v. United States, 405 U.S. 150 (1972), a tacit
agreement with a key government witness that the
government would seek a sentence reduction in exchange for
the witness’s favorable testimony, and that the witness was an
informant for the Drug Enforcement Administration (DEA).
Appellants further assert that the government violated
Mooney v. Holohan, 294 U.S. 103 (1935) and Napue v.
Illinois, 360 U.S. 264 (1959), by allowing the witness to
falsely testify that there was no promise of a sentence
reduction based on the witness’s cooperation. We affirm
Appellants’ convictions and the district court’s denial of their
motion for a new trial.

I. BACKGROUND

   In a second superseding indictment, Appellants, along
with Danny Martinez (Martinez) and Walter Meneses
(Meneses), were charged with “knowingly and willfully
conspir[ing] and agree[ing] with each other to murder inmate
David Fischer . . . aka Peter Scopazzi” in violation of
6                 UNITED STATES V. RODRIGUEZ

18 U.S.C. § 1111. The indictment alleged that Appellants
armed themselves with prison-made knives (shanks) and
murdered Scopazzi in his cell. Appellants were charged with
“willfully, deliberately, and with premeditation and malice
aforethought, unlawfully kill[ing] [Scopazzi].” Appellants
were also charged with assaulting two other prison inmates,
Timothy Ultsch (Ultsch) and Wayne Rondeau (Rondeau),
with the intent to commit murder, and assault with a deadly
weapon “with the intent to do bodily harm.”

    Prior to trial, the government filed a motion in limine to
exclude evidence that medical negligence may have
contributed to Scopazzi’s death. The government maintained
that Appellants “proffered no witness, expert or otherwise,
nor any other evidence to the government that would indicate
that [Scopazzi’s] treatment by medical staff was somehow
negligent. . . .” The government also asserted that such
evidence was irrelevant because Appellants were liable for
murder irrespective of any medical negligence and that the
evidence might lead to juror confusion.

    The government also filed a related motion in limine to
preclude or limit the testimony of the defense’s medical
expert, Dr. Marshall Morgan, concerning medical
negligence.1 The government asserted that the defense’s


  1
    In a letter to the prosecution, Murillo’s attorney stated that the defense
intended to call Dr. Morgan to “testify about the nature of the stab wounds
suffered by [Scopazzi] . . . and the medical care given to [Scopazzi] by
prison and hospital personnel to treat those injuries.” “He will state that
in his opinion [Scopazzi’s] stab wounds could have been successfully
treated surgically. Furthermore, if [Scopazzi’s] condition had been
properly evaluated, the need for immediate surgery should have been
obvious.” “But because the nature of [Scopazzi’s] injuries was not
promptly or competently assessed and appropriately treated, the medical
                 UNITED STATES V. RODRIGUEZ                             7

notice did “not indicate that Dr. Morgan will state that
[Scopazzi’s] death was caused solely by the independent
intervening acts of the medical staff’s treatment. That
[Scopazzi’s] life may have been saved by more skillful
medical treatment, even if true, is legally irrelevant . . .
because even if this were true it would not relieve defendants
of responsibility for [Scopazzi’s] murder. . . .”

     In his oppositions to the government’s motions, Murillo
responded that he did “not intend to introduce evidence of
negligence as an affirmative defense to murder. . . .” Murillo
maintained that the evidence of medical negligence and Dr.
Morgan’s testimony “would further explain that the injuries
caused by the stab wounds would have been routinely
repaired with proper medical care. The nature of [Scopazzi’s]
wounds and degree of force used to cause them may be
circumstantial evidence of whether or not there was intent to
kill. . . .”

    In granting the government’s motions, the district court
held that medical negligence was not a defense to murder
charges. The district court excluded Dr. Morgan’s testimony
because Murillo failed “to proffer expert testimony that
[Scopazzi’s] death was caused solely by the independent
intervening acts of the medical staff’s treatment. . . .” The
district court held that “Dr. Morgan shall be allowed to testify
regarding the nature of [Scopazzi’s] wounds and the degree
of force used to cause them as such testimony is relevant to
the intent of the Defendants. . . .” However, Dr. Morgan was
precluded from testifying “about medical negligence in this



attention he did receive fell well below well-recognized standards of care
resulting in [Scopazzi’s] death.”
8               UNITED STATES V. RODRIGUEZ

case as the probative value of such evidence outweighs the
danger of confusing the jury.”2

    In its trial memorandum, the government sought to
introduce evidence that the motive for Appellants’ murder of
Scopazzi was Scopazzi’s disrespect of Sureños gang
members. The district court held that evidence of Appellants’
Sureños membership and the Sureños’ relationship with the
Mexican Mafia was admissible as relevant to the
government’s theory that Appellants assaulted Scopazzi due
to their Mexican Mafia connections. The district court held
that the gang affiliation evidence was more probative than
prejudicial and that the government was permitted to
introduce “a limited number of photographs of [Appellants]
posing with certain members of the Mexican Mafia, as such
evidence may go to issues of planning and preparation of the
alleged offenses, and the level of retribution called for under
the tenets of the Sureños. . . .” Appellants declined the
district court’s offer to provide a limiting instruction
concerning evidence related to the Mexican Mafia.

    At trial, Ryan Davis (Davis), a former Victorville inmate
imprisoned for being a felon in possession of a firearm and an
armed career criminal, testified that he had prior convictions
for burglary, providing false information to a police officer,
attempting to [elude] a police officer and reckless driving,
unlawful delivery of a controlled substance, and criminal
mischief. While in prison, Davis “used marijuana, meth and
heroin and drank,” and was involved in an attack on another
inmate.



  2
    The judge apparently meant to say that the probative value of the
evidence was outweighed by the danger of confusing the jury.
                 UNITED STATES V. RODRIGUEZ                          9

    According to Davis, he was not a gang member, but was
affiliated with the Aryan Brotherhood and Nazi Low Riders
and had several tattoos including swastikas and the phrase
“white power” on his chest. Despite his lack of gang
membership, Davis was “handed the keys for unit 4A,” a
prison housing unit. Davis was given this leadership position
by a member of the Aryan Brotherhood. Davis related that he
became the unit’s key holder because there were no gang
members in the unit capable of the position.

    According to Davis, Rodriguez belonged to the Sureños
and answered to the Mexican Mafia. Davis related that the
Sureños and the white inmates generally got along well and
“called each other comrades.” Davis got along well with
Rodriguez and the other Sureños. Davis testified that inmates
would have to receive permission to assault members of
another race “from the top person for their race on the yard.”
Otherwise, “their race would stab them in return.”

   On April 11, 2005, Davis noticed that Scopazzi, Ultsch,
and Rondeau had been drinking. Davis observed that
Scopazzi was still drinking during dinner. Davis had injected
methamphetamine on that day.

    Later, Davis noticed Murillo, Rodriguez, and Mujica with
another inmate, Dan Petty (Petty), in the prison yard.3
According to Davis, Petty was escorting Murillo, Rodriguez,
and Mujica through the yard so that they would not be
stopped by the guards. Davis related that it was common
practice for an inmate to escort other inmates who had


 3
   During his testimony, Davis refers to Murillo, Rodriguez, and Mujica
by their nicknames Yogi for Murillo, Lonely for Rodriguez, and Slow for
Mujica. This opinion refers to Appellants by their last names.
10             UNITED STATES V. RODRIGUEZ

weapons, alcohol, or drugs so as to create a diversion if
stopped by the guards.

    Davis subsequently met Scopazzi on the yard. Scopazzi
“was drunk, kind of hyperactive. He was shadow boxing . . .
with [Rondeau].” Murillo, Rodriguez, and Mujica “walked
up while [Scopazzi] was horse playing” and looked irritated.
Davis decided that he needed to “get [Scopazzi, Rondeau and
Ultsch] to go to bed, to go to sleep so that . . . hopefully
nothing would happen over in their side of the unit.”

    After Davis took Scopazzi and Ultsch to their cell, Robert
Salazar (Salazar) visited the cell and inquired if there were
any problems between Scopazzi and Murillo. Scopazzi joked
that he and Murillo could “go in the TV room,” meaning that
Scopazzi and Murillo could fight. Davis told Salazar that
Scopazzi was “acting up, but everything’s all right . . .”
Salazar responded, “all right guys” and “left the cell.” Davis
believed that Salazar “obviously was sizing stuff up.” After
Salazar left, Scopazzi told Davis that another inmate had
Scopazzi’s shank in the television room and Davis instructed
Rondeau to retrieve the shank.

    Murillo, Rodriguez, and Mujica entered Scopazzi’s cell
and closed the door behind them. Murillo went to the corner
of the cell with his hands under his shirt. According to Davis,
Murillo “had his teeth locked and his jaw clenched and his
eyes were focused on [Scopazzi], and he just had a real angry
look . . .” Davis told Murillo that Scopazzi had been drinking
and pleaded with Murillo, “Don’t do this.” Murillo warned
Davis to back up or he would “get stabbed, too.” Davis
noticed a piece of white sheet in Murillo’s hand, which was
“common with shanks. Davis also observed a bandana
wrapped around Mujica’s hand as Mujica moved towards
               UNITED STATES V. RODRIGUEZ                   11

Scopazzi. As Davis grabbed Mujica and pulled him to the
floor, Murillo stabbed Scopazzi. Rodriguez also had a shank
and stabbed Rondeau in the face. Davis noticed that
Rodriguez had gloves on his hands. When Ultsch returned to
the cell, he was stabbed by Rodriguez. According to Davis,
Scopazzi did not make any threatening moves or statements
prior to the altercation. Davis testified that he never learned
why Murillo, Rodriguez, and Mujica attacked Scopazzi.

    After the altercation, Davis assisted Scopazzi, who had
“puncture wounds in his chest.” Although Scopazzi told
Davis that he was all right, Davis was concerned about
Scopazzi’s breathing. Because Davis thought Scopazzi had
a punctured lung, he assisted Scopazzi in seeking medical
treatment. When Scopazzi continued to refuse medical
treatment, prison guards placed him on the ground and
shackled him.

    Davis subsequently saw Salazar in the Special Housing
Unit’s recreation area, and Salazar told Davis to inform the
FBI that Scopazzi had a knife. Davis eventually provided a
statement to the FBI and was placed in protective custody.
Davis acknowledged that termination of his sentence was
possible based on his cooperation. Davis also conceded that
he may have received a sentence reduction and been placed
in a safer environment due to his cooperation. Davis
acknowledged that he signed a letter agreement with the
government requiring Davis to testify truthfully. According
to Davis, the letter agreement did not contain any promises
concerning a sentence reduction, and any leniency was not
contingent upon the trial’s outcome.

    Regarding Davis’ testimony, the district court instructed
the jury that Davis “may have received, or may receive,
12             UNITED STATES V. RODRIGUEZ

benefits from the government in connection with this case.
For this reason, in evaluating the testimony . . . [the jury]
should consider the extent to which or whether that witness’s
testimony may have been influenced by this factor. In
addition, [the jury] should examine [Davis’] testimony with
greater caution than that of other witnesses.”

    Dr. Glenn Holt, a medical examiner for San Bernardino
County, performed the autopsy on Scopazzi. Dr. Holt
observed that there were five puncture wounds on Scopazzi’s
body. The first puncture wound was approximately three
inches deep and “went through the skin, soft tissue, and
muscle and hit the third rib and caused some hemorrhage
above and below the third rib and also in the muscle between
the third and fourth ribs. . . .” The second puncture wound
was “a little over three inches” deep and penetrated
Scopazzi’s right lung, causing the lung to collapse. The third
puncture wound was approximately five inches deep and
entered the peritoneal cavity creating a hole in the liver. The
fourth puncture wound was approximately “two and a third
inches” deep and penetrated the muscle wall into the
peritoneal cavity. The fifth puncture wound was “a third of
an inch” deep in Scopazzi’s right upper arm.

    Dr. Holt opined that the cause of Scopazzi’s death was a
“sequelae of puncture wounds of torso” and “the sequelae
[were] events following an initial event, so . . . the injuries
occur and during events subsequently there were
complications that led to his death.” Dr. Holt related that
“there were some complications that flowed from the fact that
                 UNITED STATES V. RODRIGUEZ                           13

[Scopazzi] was stabbed” and that those complications led to
his death.4

    Officer Robert Riley, a Bureau of Prisons correctional
officer, testified that he was working at the Special Housing
Unit in April, 2005. On April 14, 2005, Officer Riley
searched Murillo’s cell and found a small note referred to as
a “kite” in “a baby powder bottle.” According to a stipulated
translation of the kite, Murillo stated that Scopazzi had
“disrespected the ‘Sur,’” that Scopazzi and the other inmates
“got what they had coming, cause [sic] I’m 100% Rider
homeboy. . . .”

    Special Agent Daniel Evanilla of the California
Department of Corrections and Rehabilitation testified as an
expert on prison gangs. According to Agent Evanilla,
“Sureños are Hispanic gang members that, when they go to a
prison or a county jail, band together as a group. . . .” Agent
Evanilla related that “the Sureños are the recruitment pool for
the Mexican Mafia,” and “[t]hey are considered the foot
soldiers for the Mexican Mafia.” “The Sureños conduct
criminal activities for the Mexican Mafia prison gang. They
respond to . . . the edicts and the orders of the Mexican Mafia
prison gang in terms of their criminal activities, their rules,
their regulations and how they conduct themselves in prison.”
Agent Evanilla testified that respect from other prisoners was
an important element of the Sureños’ credo and disrespect
was “not tolerated.” Disrespect from a member of another
race, particularly when witnessed by other Sureños, was “a
major factor” in the Sureños’ culture. According to Agent


 4
  During cross-examination, the district court sustained objections to the
defense’s questions concerning the specific complications that led to
Scopazzi’s death and whether brain swelling was the major complication.
14             UNITED STATES V. RODRIGUEZ

Evanilla, the reprisal for such disrespect would be “[s]ome
violent assault.” Agent Evanilla reviewed the kite that was
discovered by prison officials in Murillo’s cell and
interpreted the kite as meaning that the white inmates had
disrespected the Sureños.

    Captain Robert Hodak of the Englewood Federal
Correctional Institution also testified that the Sureños were
“the foot soldiers for the Mexican Mafia.” According to
Captain Hodak, Salazar was an influential member of the
Sureños and was considered a “[comrade] of the Mexican
Mafia.” Captain Hodak investigated the assault on Scopazzi.
After reviewing the video of the inmates prior to the assault,
Captain Hodak opined that, based on demeanor, positioning,
and body language, Meneses and Martinez served as
lookouts.

    Salazar testified that he was serving sentences for armed
bank robbery and possession of contraband. He confirmed
that he was a Sureño, and that the Mexican Mafia controls the
Sureños “to an extent.” According to Salazar, the white
inmates and the Sureños were “friendly” and “would hang out
together.”

    On April 11, 2005, Salazar and Scopazzi started to drink
wine together “right after breakfast . . . approximately 7 in the
morning.” Scopazzi became “overly drunk. He was loud.
He was being physical with people . . . hitting on people. . . .”
Salazar had never before observed Scopazzi in this condition.

    Murillo told Salazar that Scopazzi “had disrespected
[Murillo] in a sense where he was using the restroom on the
toilet and [Scopazzi] opened the door and said something to
the effect of, I could’ve got you, something like that.”
               UNITED STATES V. RODRIGUEZ                    15

Although Murillo and Scopazzi were friends, Murillo was
“upset about what happened.” Salazar went to Scopazzi’s cell
to talk to him. Salazar intended to tell Scopazzi that Scopazzi
“was drunk, and that he was disrespecting people and he
needed to go to sleep.” Salazar asked Scopazzi “what’s up
with you and [Murillo]?” According to Salazar, Scopazzi
jokingly said that he and Murillo could go to the television
room and fight. Scopazzi eventually apologized. Salazar did
not observe any shanks or other weapons in Scopazzi’s cell.

    After speaking with Scopazzi, Salazar informed Murillo
that Scopazzi had apologized, and suggested that Murillo talk
to Scopazzi the next day when Scopazzi was no longer
intoxicated. However, Murillo “was upset over the
disrespect and he felt that he had that apology coming from
[Scopazzi] . . .” According to Salazar, he did not know that
Scopazzi was going to be harmed and did not realize that
Scopazzi had been stabbed until after the incident. Although
he described himself as a mediator, Salazar acknowledged
that he did not accompany Murillo to Scopazzi’s cell.

   After the assault on Scopazzi, Salazar observed a shank
in Rodriguez’s cell. Rodriguez did not tell Salazar that
Scopazzi had attacked them. Salazar learned that Scopazzi
had been stabbed from “the white guys on the tier.”

    Murillo testified that, while he was using the toilet in his
cell, Scopazzi entered Murillo’s cell and “put his hands on his
waist” and said, “I could have got you slipping . . .” Murillo
thought that Scopazzi “was playing around.” Later in the
day, Scopazzi entered Murillo’s cell with Ultsch and
Scopazzi “mov[ed] his body back and forth like he wanted to
punch [Murillo] . . .” Murillo did not believe that “they were
playing around anymore.”
16             UNITED STATES V. RODRIGUEZ

    Murillo talked to Salazar because he “didn’t want this to
escalate into a bigger problem.” Murillo told Salazar that
“[t]hese guys keep coming to my cell and disrespecting
me. . . .” Although Salazar told Murillo that Scopazzi had
apologized, Murillo went to Scopazzi’s cell for a direct
apology. Murillo denied having a shank when he went to
Scopazzi’s cell. According to Murillo, Scopazzi started
swearing at Murillo and reached for a shank. According to
Murillo, he disarmed Scopazzi and used Scopazzi’s shank to
stab Scopazzi in self-defense.

    Rodriguez testified that, when Rodriguez, Murillo, and
Mujica went to Scopazzi’s cell, they did not have any shanks.
Scopazzi started to scream at them when they entered the cell
and Rodriguez thought that Rondeau had a shank, although he
never saw it. According to Rodriguez, he saw a shank tucked
into Scopazzi’s waistband.

    James Reed Harris (Harris), an inmate at the Victorville
federal prison who was serving sentences for bank robbery
and “weapons, assault,” testified that he was Davis’ cellmate
on the day of the assault.               Davis had injected
methamphetamine at least twice, had not slept for four days,
and was “getting real paranoid.” Harris described Davis as
“acting rational enough,” but Harris was concerned that Davis
“might fall over . . .” Harris explained that he was “testifying
because Ryan Davis [was] lying to get a time cut.”

    The jury convicted Murillo and Rodriguez of conspiracy
to commit murder, first degree murder, and assault with a
dangerous weapon with intent to do bodily harm as to Ultsch
and Rondeau. The jury acquitted Murillo and Rodriguez of
assault with intent to commit murder as to Ultsch and
Rondeau.
                UNITED STATES V. RODRIGUEZ                     17

    The jury convicted Mujica of conspiracy to commit
murder and first degree murder, but acquitted Mujica of
assault with intent to commit murder and assault with a
dangerous weapon with intent to do bodily harm as to Ultsch
and Rondeau.

    Appellants filed a motion for new trial because the
government failed to disclose that Davis had received an
undisclosed sentence reduction and had served as a DEA
informant.5 Appellants maintained that Davis had a tacit
agreement with the government for a sentence reduction
because the government sought to reduce Davis’ sentence on
the same day as the verdicts were rendered. The motion was
denied.

    Appellants filed timely notices of appeal.

II. STANDARDS OF REVIEW

    “We review de novo whether an evidentiary error rises to
the level of a constitutional violation. . . .” United States v.
Pineda-Doval, 614 F.3d 1019, 1032 (9th Cir. 2010) (citation
omitted).

    “We review the district court’s evidentiary rulings for
abuse of discretion and its underlying factual determinations
for clear error.” United States v. Lukashov, 694 F.3d 1107,
1114 (9th Cir. 2012) (citation omitted).

   “We review de novo a district court’s denial of a new trial
motion based on a Brady violation.” United States v.

  5
    We granted a limited remand for the district court to consider
Appellants’ motion.
18              UNITED STATES V. RODRIGUEZ

Sedaghaty, 728 F.3d 885, 899 (9th Cir. 2013) (citation
omitted). “Likewise, the question of materiality is a legal
matter that we review de novo.” Id. (citations, alteration, and
internal quotation marks omitted).

   We also review de novo the district court’s denial of a
new trial based on an asserted Mooney-Napue violation. See
United States v. Houston, 648 F.3d 806, 814 (9th Cir. 2011).

III.      DISCUSSION

       A. Medical Evidence Concerning Scopazzi’s Death

    Appellants contend that the district court denied them a
complete defense by improperly excluding evidence that
gross medical negligence and Scopazzi’s removal of his
breathing tube contributed to Scopazzi’s death. Appellants
maintain that the excluded medical evidence was relevant to
Appellants’ defense that the stab wounds were not the
proximate cause of Scopazzi’s death and that they lacked the
requisite intent to kill Scopazzi.

     The resolution of Appellants’ evidentiary challenge is
largely controlled by our decision in Pineda-Doval. In that
case, Pineda-Doval challenged his convictions for “ten counts
of transportation of illegal aliens resulting in death.” Pineda-
Doval, 614 F.3d at 1022. He maintained that “the jury should
have been instructed that it could find the defendant guilty
only if his conduct was the proximate cause of the ten
charged deaths. . . .” Id. Pineda-Doval argued that the
proximate cause of the aliens’ death was the negligent
deployment by Border Patrol agents of a spike strip that
caused the defendant’s vehicle to flip over. See id. at 1024.
Prior to trial, the district court granted the government’s
               UNITED STATES V. RODRIGUEZ                    19

motion in limine to exclude as irrelevant evidence that the
Border Patrol agents had failed to comply with the requisite
procedures for deployment of the spike strip. See id.

    Pineda-Doval argued that the district court failed to
properly instruct the jury that the “resulting in death” element
required proof that his acts were the proximate cause of the
aliens’ deaths. Id. at 1025. We observed that “[a] basic tenet
of criminal law is that, when a criminal statute requires that
the defendant’s conduct has resulted in an injury, the
government must prove that the defendant’s conduct was the
legal or proximate cause of the resulting injury. . . .” Id. at
1026 (citation and internal quotation marks omitted). We
explained that proof of proximate cause required a showing
by the government that the harm suffered by the victim was
a foreseeable outcome of the defendant’s conduct. See id. at
1028. The proximate cause showing is more easily met when
the intervening event is “not a coincidence or unrelated to the
defendant’s prior conduct, but rather was a response to that
conduct.” Id. When the intervening event is a response to the
defendant’s conduct, “the question is whether the intervening
act was abnormal—that is, whether, looking at the matter
with hindsight, it seems extraordinary. . . .” Id. (citation
omitted). We held:

           Pineda-Doval’s failed attempt to swerve
       around the spike strip was the proximate
       cause of the deaths of ten individuals. It was
       entirely foreseeable that the Border Patrol
       would deploy a [spike strip] against the
       defendant’s Suburban and that Pineda-Doval’s
       dangerous driving would end in an
       accident. . . . No reasonable jury could have
20             UNITED STATES V. RODRIGUEZ

       found that a car accident was an extraordinary
       result.

Id. at 1029.

    We rejected the defendant’s argument that the Border
Patrol agents’ negligence “constituted a superseding cause of
the accident. . . .” Id. at 1029. We opined:

       If we assume that [the Border Patrol agent]
       made a mistake by pulling the [spike strip]
       across the road several seconds too early, this
       mistake was not so extraordinary as to break
       the chain of causation. Pineda-Doval created
       the dangerous conditions . . . and, because he
       refused to pull over in response to [the Border
       Patrol agent’s] lights and sirens, forced the
       Border Patrol to use drastic measures to
       stop him. The resulting deaths of his
       ten passengers were tragic, but not
       unexpected. . . .

Id. at 1029–30.

     We held that any error in the district court’s exclusion of
evidence that the Border Patrol agents were negligent in
failing to follow the requisite procedures for deployment of
the spike strip was harmless. “[O]ccasional negligence that
should have been anticipated by the defendant does not defeat
proximate cause. . . .” Id. at 1029 (citation and internal
quotation marks omitted). “To show that the actions of [the
Border Patrol agent] constituted a superseding cause that
broke the chain of causation between Pineda-Doval’s
dangerous driving, that negligence would have had to be so
               UNITED STATES V. RODRIGUEZ                   21

extraordinary that it would be unfair to hold the defendant
responsible for the resulting accident and deaths.” Id. at 1034
(citation and internal quotation marks omitted). “Even
assuming that the defendant persuaded the jury that timing
was essential to the correct and safe deployment of [the spike
strip] and that [the Border Patrol agent] made the mistake of
pulling the spike strip across the road several seconds too
early, no reasonable jury could have found that [the Border
Patrol agent’s] actions were extraordinary and could not have
been foreseen by [the defendant].” Id. (citations and footnote
reference omitted). Therefore,“[t]he district court’s error in
excluding evidence of [the Border Patrol] policies on spike
strips was harmless beyond a reasonable doubt.” Id.

    Similarly, in this case we conclude that any error in the
district court’s exclusion of evidence concerning medical
negligence or Scopazzi’s removal of his breathing tube was
harmless beyond a reasonable doubt. Because medical
treatment was a foreseeable response to Appellants’ conduct
of stabbing Scopazzi, proximate cause was established by the
government. See id. at 1028. Appellants failed to proffer
evidence establishing medical negligence as a superseding
cause of Scopazzi’s death. To make the required showing,
Appellants would have to demonstrate that medical
negligence and Scopazzi’s removal of his breathing tube were
“so extraordinary that it would be unfair to hold [Appellants]
responsible for the resulting . . . death[ ].” Pineda-Doval,
614 F.3d at 1034 (citation and internal quotation marks
omitted); see also Mitchell v. Prunty, 107 F.3d 1337, 1341
n.8 (9th Cir. 1997), as amended, overruled on other grounds
by Santamaria v. Horsley, 133 F.3d 1242, 1248 (9th Cir.
1998) (observing that “if gross maltreatment of the wound
was the sole cause of death, the person inflicting the wound
will not be liable, because the wound was not the proximate
22             UNITED STATES V. RODRIGUEZ

cause of death. In this case, gross maltreatment would have
been required to render [the victim’s] gunshot wounds fatal.”)
(citation and internal quotation marks omitted).

    As it was foreseeable in Pineda-Doval that Border Patrol
agents would deploy a spike strip to stop a fleeing suspect, it
was similarly foreseeable in this case that a victim of multiple
deep stab wounds would receive medical care. See Pineda-
Doval, 614 F.3d at 1034. And, as we held in Pineda-Doval,
any negligence in the foreseeable response to the stab wounds
does not break the causation chain. See id. The same is true
regarding Scopazzi’s removal of his breathing tube. See
Sedation and Delirium in the Intensive Care Unit, 14 New
England J. of Med. 444 (Jan. 30, 2014) (discussing the
accidental removal of endotracheal tube due to delirium and
agitation); see also Peter Pressman, M.D., Delirium: An Acute
Confusional State, April 23, 2014 (observing that “[a]cute
confusional state, also known as delirium or encephalopathy,
is so common in hospitals that it’s almost seen as routine by
many hospital staff. Between 14 to 56% of all hospitalized
patients develop confusion. Intubated patients in the
intensive care unit have an even higher rate, reaching about
82%. . . . Such agitated patients may also try to remove tubes
or IV lines that are providing life-saving medications.”)
(available at      http://neurology.about.com/od/Delirium/a/
Delirium.htm)(last visited May 8, 2014).

    Dr. Morgan’s proffered testimony did not address whether
medical negligence was the sole cause of Scopazzi’s death or
even an intervening cause. Although Dr. Morgan purportedly
opined that “the medical attention [Scopazzi] did receive fell
well below well-recognized standards of care resulting in
[Scopazzi’s] death,” Dr. Morgan did not state that
extraordinary medical negligence or Scopazzi’s removal of
               UNITED STATES V. RODRIGUEZ                   23

his breathing tube caused Scopazzi’s death independent of the
stab wounds themselves. Although the district court ruled
that Dr. Morgan could testify “regarding the nature of
[Scopazzi’s] wounds and the degree of force used to cause
them,” Dr. Morgan never actually testified. Appellants also
informed the district court that they did not intend to rely on
medical negligence as an affirmative defense. Thus, the
district court’s exclusion of Appellants’ proffered evidence
had no bearing on the fairness of Appellants’ trial because
that evidence did not establish medical negligence or removal
of the breathing tube as a superseding cause of Scopazzi’s
death.

    Our conclusion that Appellants failed to proffer
admissible evidence that extraordinary medical negligence or
Scopazzi’s removal of his breathing tube constituted a
supervening cause of Scopazzi’s death is bolstered by the
Seventh Circuit’s rationale in Brackett v. Peters, 11 F.3d 78
(7th Cir. 1993). In Brackett, the habeas petitioner was
convicted of felony murder based on his rape and assault of
an 85-year-old woman. See id. at 79. The victim “was
admitted to the hospital with a broken arm, a broken rib, and
extensive bruises. During her stay in the hospital, which
lasted several weeks, she—described as feisty before the rape
and beating—became depressed, resisted efforts to feed her,
and became progressively weaker.” Id. (internal quotation
marks omitted). After her transfer to a nursing home, she
continued to regress, even though her physical injuries were
healing. Because of her lack of appetite, her doctor ordered
placement of a nasal gastric feeding tube. However, the tube
could not be inserted, in part because the victim’s facial
injuries made insertion of the tube too painful. See id.
Approximately ten days after her admission, the victim died
when a large quantity of food became lodged in her trachea,
24             UNITED STATES V. RODRIGUEZ

asphyxiating her. See id. The habeas petitioner contended
that the negligence of the nurse who was feeding the victim
caused her death. See id. at 80.

    In rejecting the habeas petitioner’s argument and holding
that the petitioner’s assault was the proximate cause of the
victim’s death, the Seventh Circuit observed that “an act is a
cause of an event if two conditions are satisfied: the event
would not have occurred without the act; the act made the
event more likely.” Id. at 79. The Seventh Circuit opined
that the nurse’s purported negligence was nothing more than
another cause of the victim’s death. See id. at 80. The
Seventh Circuit concluded that “a murderer does not avoid
conviction by pointing out that his act was only one of many
causes that concurred to bring about his victim’s death.” Id.
“It is enough if his act was one of the causes-enough
therefore if [the petitioner’s] assault made [the victim’s]
death more likely and if, but for the assault, she would not
have died as soon as she did. . . .” Id. (citations omitted).
“Death was the last link in a continuous series of events that
began with the assault. [The victim] died a month later, never
having returned home. . . .” Id. The court emphasized that
had the victim never been assaulted, it is unlikely that she
would have been admitted to the hospital to die one month
later. See id.

    The petitioner also argued that the assault caused the
victim to become clinically depressed and suicide-prone.
According to the petitioner, the victim committed suicide by
refusing to eat, and that suicide was a superseding cause of
the victim’s death. See id. at 80–81. The Seventh Circuit
rejected this argument, reasoning that “[t]he fact that a
psychiatric condition, whether or not by precipitating suicide,
is one of the causes of a victim’s death does not excuse his
               UNITED STATES V. RODRIGUEZ                    25

murderer. Otherwise, it would be open season on sufferers
from mental illness.” Id. at 81 (citations omitted). The court
contrasted a chance occurrence, such as a fire at a nursing
home, that would be a superseding cause if death resulted.
See id. at 80.

    Other circuits have also held that defendants are liable for
murder notwithstanding additional occurrences. For example,
in United States v. Swallow, 109 F.3d 656 (10th Cir. 1997),
the Tenth Circuit affirmed the defendant’s murder
convictions despite the defendant’s argument that the district
court erred in failing to provide a “proposed instruction
characteriz[ing] an independent intervening cause as the
unforeseeable gross negligence of a third party that relieves
the defendant of responsibility for the death of the
victim. . . .” Id. at 659 (citations omitted). In rejecting the
defendant’s argument that negligence on the part of rescuers
contributed to the victims’ deaths, the Tenth Circuit held that
“in cases involving death from injuries inflicted in an assault,
courts have uniformly held that the person who inflicted the
injury will be liable for the death despite the failure of third
persons to save the victim.” Id. at 660 (citations and
alteration omitted).

    Similarly, in United States v. Guillette, 547 F.2d 743 (2d
Cir. 1976), the Second Circuit held that the defendant was
liable for the death of a victim who may have accidently
triggered a bomb. See id. at 747–48. “The trial judge
instructed the jury that even if [the victim] died accidentally
through his own actions, the defendants would nonetheless be
guilty of conspiracy with death resulting if [the victim’s]
death was induced or brought about by some act of a
conspiracy in furtherance of the purposes of a conspiracy.”
Id. at 748. The Second Circuit ruled that “[a] fundamental
26             UNITED STATES V. RODRIGUEZ

principle of criminal law is that a person is held responsible
for all consequences proximately caused by his criminal
conduct. The concept of proximate cause incorporates the
notion that an accused may be charged with a criminal
offense even though his acts were not the immediate cause of
the victim’s death or injury.” Id. at 749 (citation omitted).
“In many situations giving rise to criminal liability, the death
or injury is not directly caused by the acts of the defendant
but rather results from intervening forces or events, such as
negligent medical treatment, escape attempts, or the negligent
or intentional acts of a third party.” Id. “Where such
intervening events are foreseeable and naturally result from
a perpetrator’s criminal conduct, the law considers the chain
of legal causation unbroken and holds the perpetrator
criminally responsible for the resulting harm.” Id. (citations
omitted); see also United States v. Rodriguez, 279 F.3d 947,
950–51 (11th Cir. 2002) (holding in the sentencing
enhancement context that “one may be held criminally liable
for a victim’s death even where medical negligence or
mistreatment also contributed to the victim’s death”) (citation
omitted).

    State courts have also consistently held that the defendant
must demonstrate extraordinary medical negligence as the
sole cause of death to break the causation chain. See, e.g.,
People v. Mars, 985 N.E.2d 570, 575 (Ill. App. Ct. 2012), as
modified (“The presumption [of causation] must be rebutted
by the defendant’s presentation of contrary evidence that the
sole cause of death was the intervening gross negligence of
physicians. Unskilled or improper medical treatment that
aggravates a victim’s preexisting condition or contributes to
the victim’s death is considered reasonably foreseeable and
does not constitute an intervening act unless the treatment is
so bad that it can be classified as gross negligence or
               UNITED STATES V. RODRIGUEZ                     27

intentional malpractice. . . .”) (citations omitted) (emphasis in
the original); State v. Shabazz, 719 A.2d 440, 445 (Conn.
1998) (“The rule . . . that such gross negligence may permit
the defendant to escape liability when it was the sole cause of
the death, strikes an appropriate balance between the notions
of criminal responsibility for one’s conduct, on one hand, and
intervening cause, on the other.”) (citation omitted); State v.
Kirby, 39 P.3d 1, 12 (Kan. 2002) (“It is clear that the
physicians’ actions were not so unusual, abnormal, or
extraordinary that they could not have been foreseen. The
physicians’ negligence, if any, did not supersede the effect of
the wounds inflicted by [the defendant] so as to become the
sole legal cause of [the victim’s] death.”); People v. Roberts,
826 P.2d 274, 295 (Cal. 1992) (in bank), as modified (“If a
person inflicts a dangerous wound on another, it is ordinarily
no defense that inadequate medical treatment contributed to
the victim’s death. To be sure, when medical treatment is
grossly improper, it may discharge liability for homicide if
the maltreatment is the sole cause of death and hence an
unforeseeable intervening cause. . . .”) (citations omitted).

    Given the weight of such consistent federal and state
precedent, we conclude that Appellants failed to proffer any
probative evidence that extraordinary medical negligence or
Scopazzi’s removal of his breathing tube was the sole cause
of Scopazzi’s death. Indeed, Scopazzi would not have
needed medical care or a breathing tube absent Appellants’
infliction of five stab wounds, including a wound that
punctured Scopazzi’s lung. The alleged medical negligence
or removal of Scopazzi’s breathing tube may have been
“another cause of [Scopazzi’s] death,” but neither was a
supervening event exonerating Appellants from the death
resulting from their assault. Brackett, 11 F.3d at 80 (citations
omitted). It was not sufficient for Appellants to simply
28                UNITED STATES V. RODRIGUEZ

proffer some evidence of medical negligence or Scopazzi’s
removal of his breathing tube without otherwise satisfying the
standard for proximate cause. See Pineda-Doval, 614 F.3d at
1034; see also Guillette, 547 F.2d at 749 (“Where such
intervening events are foreseeable and naturally result from
a perpetrator’s criminal conduct, the law considers the chain
of legal causation unbroken and holds the perpetrator
criminally responsible for the resulting harm. This principle
applies even where the direct cause of death is a force set in
motion by the victim himself. . . .”) (citations omitted).6

    United States v. Main, 113 F.3d 1046 (9th Cir. 1997) does
not compel a contrary result. In Main, we delineated the
applicable standard for proximate cause involving an
involuntary manslaughter conviction resulting from the
defendant’s reckless driving while intoxicated. See id. at
1047. In reversing the conviction, we held that the district
court failed to properly instruct the jury that it must find that
the defendant’s acts were the proximate cause of the victim’s
death. See id. at 1049–50. We observed that “[a]ll of the
authorities agree that to be guilty of involuntary manslaughter

 6
   Consistent with its prior rulings on the government’s motions in limine,
the district court did not abuse its discretion when it denied Appellants’
request to cross-examine Dr. Holt, the medical examiner, regarding his
description of “the sequelae of puncture wounds” ultimately leading to
Scopazzi’s death. Appellants specifically sought to question Dr. Holt
concerning Scopazzi’s removal of his breathing tube, a sudden loss of
blood, cardiac arrest, and brain swelling. Dr. Holt’s testimony did not
open the door to this additional medical evidence because Dr. Holt
acknowledged that the complications “flowed from the fact that
[Scopazzi] was stabbed.” In any event, Appellants’ proffer did not satisfy
the proximate cause standard of complications “so extraordinary that it
would be unfair to hold [Appellants] responsible for the resulting . . .
death[ ].” Pineda-Doval, 614 F.3d at 1034 (citation and internal quotation
marks omitted); see also Brackett, 11 F.3d at 80.
                 UNITED STATES V. RODRIGUEZ                           29

the harmful result must be within the risk foreseeably created
by the accused’s conduct; if the physical causation is too
remote, the law will not take cognizance of it. . . .” Id. at
1049. We considered the foreseeability determination more
difficult when the manslaughter charges stem from excessive
speed or drunk driving because many individuals speed
and/or drive while impaired without killing anyone. See id.
Therefore, the foreseeability determination would require
careful examination of the individual “conduct engaged in.”
Id. We held that reversal of the conviction was warranted
because “[w]hen the jury is not told that it must find that the
victim’s death was within the risk created by the defendant’s
conduct an element of the crime has been erroneously
withdrawn from the jury.” Id. at 1050 (citations omitted).7

    In stark contrast to Main, Appellants’ convictions were
not premised on the more ambiguous acts of “excessive speed
or drunk driving.” Main, 113 F.3d at 1049. Rather,
Appellants’ use of deadly weapons to directly inflict serious
stab wounds carried the completely foreseeable risk that
Scopazzi’s injuries would result in death. Moreover, the
district court included the concept of proximate cause in the




  7
    We offered the following example of a sufficient intervening cause:
“Suppose [the victim] had been pinned in the wreck and then eaten by a
bear. His death would have been the result of the wreck; but for [the
defendant’s] driving, he would not have been killed, yet a jury could find
as a fact that the death was not within the risk that [the defendant] had
created. In the language of the American Law Institute death from a bear
was not within the risk foreseeably created by the reckless driving[.]”
Main, 113 F.3d at 1049 (citation omitted).
30                UNITED STATES V. RODRIGUEZ

instruction on voluntary manslaughter, and the concept of
foreseeability in other instructions.8

    Because Appellants failed to demonstrate that any
medical negligence or removal of a breathing tube was “so
extraordinary that it would be unfair to hold [Appellants]
responsible for the resulting . . . death[ ],” Pineda-Doval,
614 F.3d at 1034 (citation and internal quotation marks
omitted), and because the jury instructions included the
concepts of foreseeability and proximate cause, the district
court acted within its discretion when it cabined the medical
evidence.

       B. Evidence of Gang Affiliation

    Appellants next contend that the district court erred in
admitting irrelevant and prejudicial evidence concerning
Appellants’ alleged connection to the Mexican Mafia.
Appellants also maintain that the district court erred in
holding that the evidence’s probative value outweighed any
prejudice under Federal Rule of Evidence 403.


   8
      Appellants’ reliance on United States v. Chouteau, 102 U.S. 603
(1880) is also misplaced. In Chouteau, the Supreme Court considered
whether a distiller was liable for breach of certain bond conditions. See
id. at 608. Within that context, the Supreme Court merely observed that
“[i]f, for example, a party should charge another with inflicting upon his
person a wound by which he lost an arm, it would be a good defence to
show that the loss resulted from unskilful medical treatment or neglect and
not from the wound inflicted. So here, it is enough for the sureties to
show that the loss to the government was produced by other means than
the particular breach of duty by their principal, of which the government
complains. . . .” Id. at 609. Needless to say, the law has evolved in the
century-plus since Chouteau was decided. See Pineda-Doval, 614 F.3d
at 1034.
               UNITED STATES V. RODRIGUEZ                   31

    In United States v. Santiago, 46 F.3d 885 (9th Cir. 1995),
we rejected an analogous evidentiary challenge. In that case,
to establish the motive for the defendant’s first degree murder
of another inmate, the government introduced a cellmate’s
testimony that the defendant sought to become a member of
the Mexican Mafia. See id. at 887–88. In affirming the
district court’s admission of evidence concerning the
defendant’s ties to the Mexican Mafia, we observed that the
testimony did not violate Rule 404(b) because it “did not
relate to other crimes,” and it fell within the exception for
evidence regarding motive. Id. at 888–89. “[T]he testimony
relating to the Mexican Mafia was necessary to explain the
reason that Santiago would kill a stranger – to be accepted
into the gang – and to show how and why other inmates
assisted him in obtaining the weapon.” Id. at 889. We
rejected the argument that the government’s use of the
testimony was a pretense intended to denigrate the defendant
for his affiliation with a prison gang. See id. at 889–90.
Because the evidence reflected that the defendant had
expressed interest in the gang and had associated with gang
members, including on the night before the murder, a
sufficient foundation was laid to admit the testimony. See id.
at 890.

    We similarly conclude that testimony relating to the
Mexican Mafia was relevant to Appellants’ murder of
Scopazzi, and that its probative value was not substantially
outweighed by any prejudice. Although Appellants attempt
to distinguish Santiago on the basis that the government did
not present any evidence that Appellants stabbed Scopazzi
based on their ties to the Mexican Mafia, the record supports
a contrary conclusion. As in Santiago, the Mexican Mafia
testimony was critical to the government’s theory that
Appellants did not act in self-defense and that their attack on
32             UNITED STATES V. RODRIGUEZ

Scopazzi for seemingly insignificant acts of disrespect was
motivated by their ties to the Mexican Mafia. See Santiago,
46 F.3d at 889–90. The government also introduced the kite
from Murillo’s cell that implied the attack on Scopazzi was
motivated by Scopazzi’s disrespect of the Sureños.

    Appellants’ trial was also permeated with references to
their gang affiliations, and Agent Evanilla’s expert testimony
addressed the connection between the Sureños and the
Mexican Mafia within the prison gang hierarchy. Given
Appellants’ admitted gang connections, the expert testimony
concerning the Mexican Mafia and photographs of Appellants
with members of the Mexican Mafia was not unduly
prejudicial as “the Mexican Mafia was not the entire theme of
the trial, so as to infect the trial with the threat of guilt by
association. . . .” Santiago, 46 F.3d at 889 (citation,
alteration, and internal quotation marks omitted). This is
particularly true in this case where the trial focused primarily
on the events that transpired in Scopazzi’s cell and the jury
was presented with numerous photographs and videos of the
events without reference to Appellants’ connections to the
Mexican Mafia.

    Notably, the district court also took several steps to
minimize any undue prejudice. In particular, the district court
permitted only “a limited number of photographs of
[Appellants] posing with certain members of the Mexican
Mafia” and “brief testimony by qualified witnesses regarding
the hierarchy, customs, practices and tenets of the Mexican
Mafia and its relationship and connection to the Sureños.”
The district court also committed to “include in its voir dire
of prospective jurors examination on this subject and its
effect, if any, on any juror’s ability to judge the case fairly
and objectively.” Appellants rejected the district court’s offer
               UNITED STATES V. RODRIGUEZ                     33

to provide a limiting instruction concerning why the Mexican
Mafia testimony was being admitted into evidence. See
United States v. Decoud, 456 F.3d 996, 1012 (9th Cir. 2006)
(rejecting evidentiary challenge in part because the defendant
“did not take up the district court on its offer to provide the
jury with a limiting instruction that could have mitigated, if
not negated, [the defendant’s] concerns”).

    We conclude that the district court did not abuse its
discretion in admitting evidence pertaining to the connection
between the Sureños and the Mexican Mafia as relevant to
Appellants’ motive in attacking Scopazzi. See Santiago,
46 F.3d at 889–90; see also United States v. Major, 676 F.3d
803, 810 (9th Cir. 2012) (holding that the district court did
not abuse its discretion in admitting gang affiliation evidence
as relevant to motive).

     Appellants’ reliance on Kennedy v. Lockyer, 379 F.3d
1041 (9th Cir. 2004), as amended, Spivey v. Rocha, 194 F.3d
971 (9th Cir. 1999), and Dawson v. Delaware, 503 U.S. 159
(1992) is misplaced as those cases are entirely
distinguishable. In Kennedy, we did not address an
evidentiary challenge to gang affiliation evidence. Instead,
we held that a habeas petitioner was prejudiced because the
attorney for his retrial was not provided a complete trial
transcript that included the trial court’s prior ruling excluding
such evidence. See Kennedy, 379 F.3d at 1042–43. Because
the prosecution elicited the precluded testimony in the second
trial in violation of the trial court’s prior order, we held that
the petitioner was prejudiced in part because “where, as here,
gang evidence is proffered to prove a substantive element of
the crime (and not for impeachment purposes), it would likely
be unduly prejudicial. . . .” Id. at 1056 (citation and internal
quotation marks omitted).
34             UNITED STATES V. RODRIGUEZ

     In Spivey, we considered whether the trial court erred in
excluding evidence of the witnesses’ gang affiliation
proffered by the defendant. See Spivey, 194 F.3d at 977. The
trial court excluded the evidence because it did not support
the defendant’s assertion that the victim “was killed by a
phantom killer” and there was already sufficient evidence of
the witness’s potential bias. Id. We held that, because the
evidence was purely speculative, exclusion of the evidence
did not render the defendant’s trial fundamentally unfair. See
id. at 979. Contrary to Appellants’ assertion, Spivey did not
hold that the prosecution was required to establish that gang
affiliation was the actual motive for the murder. Instead, we
articulated that, under California law, “[i]n order for evidence
of another suspect to be admissible . . . there must be direct or
circumstantial evidence linking the third person to the actual
perpetration of the crime. Motive or opportunity is not
enough. . . .” Spivey, 194 F.3d at 978 (citations and internal
quotation marks omitted).

    In Dawson, the Supreme Court held that evidence
concerning the Aryan Brotherhood was inadmissible because
it contravened the defendant’s associational rights. See
Dawson, 503 U.S. at 164–65. The Supreme Court opined that
“the Aryan Brotherhood evidence was not tied in any way to
the murder of [the defendant’s] victim” and that “the
inference which the jury was invited to draw . . . tended to
prove nothing more than the abstract beliefs of [a particular
Aryan Brotherhood] chapter. . . .” Id. at 166. Unlike in
Dawson, the Mexican Mafia evidence in this case was “tied
to the murder” of Scopazzi as evidence of motive.
               UNITED STATES V. RODRIGUEZ                   35

   C. Brady and Mooney-Napue Claims

       1. Non-Disclosure of A Tacit Agreement That
          Davis Would Receive A Sentence Reduction

    Appellants posit that a new trial is warranted because the
government’s failure to disclose a tacit agreement to reduce
Davis’ sentence contravened Brady. “Under Brady, the
suppression by the prosecution of evidence favorable to an
accused upon request violates due process where the evidence
is material either to guilt or to punishment.” United States v.
Stinson, 647 F.3d 1196, 1208 (9th Cir. 2011), as amended
(citation and internal quotation marks omitted). “There are
three components of a Brady violation: the evidence at issue
must be favorable to the accused, either because it is
exculpatory, or because it is impeaching; that evidence must
have been suppressed by the State, either willfully or
inadvertently; and prejudice must have ensued.” Id. (citation,
alteration, and internal quotation marks omitted). “To
determine whether prejudice exists, we look to the materiality
of the suppressed evidence. When looking to materiality, the
question is whether admission of the suppressed evidence
would have created a reasonable probability of a different
result, so the defendant must show only that the government’s
evidentiary suppression undermines confidence in the
outcome of the trial.” Id. (citation and internal quotation
marks omitted).

     The record reflects that there was no Brady violation
premised on Davis’ cooperation. Although the government
initiated the process under Federal Rule of Criminal
Procedure 35 to reduce Davis’ sentence on the same day the
jury found Appellants guilty, we are unable to conclude that
this temporal proximity alone establishes a Brady violation.
36                UNITED STATES V. RODRIGUEZ

At trial, Davis testified that early termination of his sentence
was possible based on his cooperation. Davis related that the
letter agreement required that he testify truthfully and that the
agreement did not provide any promises of leniency or a
sentence reduction contingent upon the trial’s outcome. As
reflected by Davis’ testimony, the government fully disclosed
the letter agreement and the FBI interviews.9 Appellants
failed to demonstrate that any of the government’s post-
verdict actions were inconsistent with the letter agreement or
were premised on an undisclosed tacit agreement.10

    We conclude that no Brady violation occurred because
there was no tacit agreement to disclose. See United States v.
Price, 566 F.3d 900, 910 n.11 (9th Cir. 2009) (“If the record
is conclusive that all relevant agents of the government did
not know about the Brady material, then, of course, no Brady
violation has occurred as the government has no obligation to
produce information which it does not possess or of which it


  9
    Appellants maintain that Davis falsely denied that he expected any
leniency based on his testimony. However, Appellants have not presented
any evidence of a tacit agreement for leniency or that Davis was aware of
any such agreement.
  10
      Appellants’ reliance on Sivak v. Hardison, 658 F.3d 898 (9th Cir.
2011) is unavailing. In that case, the witness testified that certain charges
were dismissed but “he did not know whether the prosecutor’s office was
involved in the dismissals.” Sivak, 658 F.3d at 904. The witness also
testified that he cooperated based on fears for his family’s safety and that
he was not “seeking any particular favoritism from State authorities in
exchange for his testimony . . .” Id. at 903 (internal quotation marks
omitted). We held that there was a Brady violation based on undisclosed
letters reflecting a tacit agreement for leniency. See id. at 909–10. Davis,
unlike the witness in Spivak, acknowledged that he hoped that his
cooperation would result in a sentence reduction and no tacit agreement
for leniency was unearthed.
                  UNITED STATES V. RODRIGUEZ                             37

is unaware. . . .”) (citation and internal quotation marks
omitted) (emphasis in the original). The district court also
cautioned the jury that Davis “may have received, or may
receive, benefits from the government in connection with this
case” and that the jury should examine Davis’ testimony
“with greater caution than that of other witnesses.”11 Davis’
credibility, therefore, was significantly undermined
irrespective of any tacit agreement for a sentence reduction.

         2. Non-Disclosure of Davis As A DEA Informant

    Appellants also argue that a new trial is required because
the government failed to disclose that Davis served as a DEA
informant.

    Although it is arguable that the government was required
to disclose this information as impeachment evidence, see
United States v. Si, 343 F.3d 1116, 1123 (9th Cir. 2003)
(observing that “these [informant] reports can be considered
favorable to [the defendant] because, as information about
[the witness’s] ongoing informant activities, they would
constitute impeachment evidence tending to show [the
witness’s] motives in testifying for the government”), its
disclosure would not “have led to a different result. . . .”
United States v. Olsen, 704 F.3d 1172, 1184 (9th Cir. 2013)
(citation omitted). As discussed, Davis’ credibility was
sufficiently undermined by the defense, given his admitted
cooperation with the prosecution, his extensive criminal


 11
    Appellants maintain that the district court’s instruction was ineffective
because it required the jury to speculate. However, it is unclear how the
district court’s instruction was ineffective as it specifically cautioned the
jury about the potential impact of any benefits Davis received for his
cooperation.
38             UNITED STATES V. RODRIGUEZ

history, and his illicit prison activities. Although the DEA
report may have further demonstrated Davis’ willingness to
cooperate with the government, Appellants do not point to
any benefits that Davis received from his cooperation,
particularly as Appellants do not rebut the government’s
representation that Davis was never classified as a DEA
informant. “The cross-examination of [Davis] raised
reasonable doubts as to his motivation for testifying and there
was sufficient impeachment evidence for the jury to question
seriously the veracity of [Davis’] original statement. Thus,
regardless of the failure to disclose the informant status of
[Davis], [Appellants] received a trial resulting in a verdict
worthy of confidence.” Gentry v. Sinclair, 705 F.3d 884, 905
(9th Cir. 2013), as amended (citation and internal quotation
marks omitted); see also Si, 343 F.3d at 1123 (holding that
information of witness’s role as an informant in unrelated
cases was not material).

       3. Mooney-Napue Violation

    Appellants contend that the government knowingly failed
to correct Davis’ false testimony that he was not promised a
sentence reduction in violation of Mooney and Napue.

    “A conviction obtained using knowingly perjured
testimony violates due process, even if the witness’s perjured
testimony goes only to his credibility as a witness and not to
the defendant’s guilt.” United States v. Houston, 648 F.3d
806, 814 (9th Cir. 2011) (citations omitted). “The
government’s failure to correct testimony that it later learns
is perjured is also a Mooney–Napue violation.” Id. (citation
omitted). “To prevail on a Mooney–Napue claim, the
defendant must show that (1) the testimony was actually
false, (2) the prosecution knew or should have known that the
                  UNITED STATES V. RODRIGUEZ                           39

testimony was actually false, and (3) that the false testimony
was material.” Id. (citation, alteration, and internal quotation
marks omitted). “In assessing materiality under Napue, we
determine whether there is any reasonable likelihood that the
false testimony could have affected the judgment of the jury;
if so, then the conviction must be set aside. Under this
materiality standard, the question is not whether the
defendant would more likely than not have received a
different verdict with the evidence, but whether in its absence
he received a fair trial, understood as a trial resulting in a
verdict worthy of confidence.” Id. (citation omitted).
“However, if it is established that the government knowingly
permitted the introduction of false testimony reversal is
virtually automatic.” Id. (citation omitted).

    Appellants’ Mooney-Napue claim is premised on their
contention that there was a tacit agreement that the
government would assist Davis in receiving a sentence
reduction based on his favorable testimony. However,
Appellants failed to proffer any evidence of a tacit agreement,
particularly as the government’s post-verdict actions were
consistent with the fully disclosed letter agreement and with
Davis’ testimony that the letter agreement was not contingent
upon the trial’s outcome. Appellants are unable to
demonstrate that Davis’ testimony “was actually false” or that
“the prosecution knew or should have known that the
testimony was actually false . . .” Id. (citation omitted). Thus,
a new trial was not warranted.12



  12
     Although Appellants maintain that cumulative error warrants a new
trial, there were no errors, cumulative or otherwise, requiring reversal of
Appellants’ convictions. See Pineda-Doval, 614 F.3d at 1036 (holding
that even if the defendant had been permitted to introduce evidence
40              UNITED STATES V. RODRIGUEZ

IV.     CONCLUSION

    The district court’s exclusion of evidence concerning
medical negligence and Scopazzi’s removal of his breathing
tube does not warrant reversal of Appellants’ convictions.
Appellants failed to demonstrate that any medical negligence
related to Scopazzi’s multiple stab wounds and his removal
of his breathing tube were the sole causes of Scopazzi’s death
or were so extraordinary and unforeseeable as to absolve
Appellants of liability for their vicious assault. The district
court did not abuse its discretion in admitting evidence of
Appellants’ connections to the Mexican Mafia to demonstrate
Appellants’ motive for murdering Scopazzi.                Expert
testimony concerning the connections between the Sureños
and the Mexican Mafia within the prison gang hierarchy and
photographs of Appellants with Mexican Mafia members did
not render their trial unfair because the district court properly
minimized any prejudice stemming from the evidence and
Appellants’ trial was replete with admissible evidence
regarding Appellants’ gang affiliations. Appellants also
failed to demonstrate that a new trial was warranted based on
the government’s failure to disclose immaterial information
regarding Davis’ sentence reduction and his cooperation in a
DEA investigation.

      AFFIRMED.




concerning proximate cause, “[t]here was no prejudice, cumulative or
otherwise”).
