                                PRECEDENTIAL

  UNITED STATES COURT OF APPEALS
       FOR THE THIRD CIRCUIT
            _____________

                No. 13-2214
               _____________

      UNITED STATES OF AMERICA

                      v.

   EBON P.D. BROWN, a/k/a E-MURDER

              Ebon P.D. Brown,
                             Appellant
               _____________

On Appeal from the United States District Court
    for the Western District of Pennsylvania
      District Court No. 2-11-cr-00193-001
District Judge: The Honorable Joy Flowers Conti

            Argued May 13, 2014

Before: SMITH, VANASKIE, and SHWARTZ,
               Circuit Judges

                      1
                (Filed: August 27, 2014)

Rebecca R. Haywood, Esq. [Argued]
Office of United States Attorney
700 Grant Street
Suite 4000
Pittsburgh, PA 15219
       Counsel for Appellee

Kimberly R. Brunson, Esq. [Argued]
Lisa B. Freeland
Office of Federal Public Defender
1001 Liberty Avenue
1500 Liberty Center
Pittsburgh, PA 15222
       Counsel for Appellant
                   ________________

                      OPINION
                  ________________


SMITH, Circuit Judge.

       Ebon Brown brings this appeal following his
conviction in the United States District Court for the
Western District of Pennsylvania of unlawful possession
of a firearm by a convicted felon, 18 U.S.C. § 922(g)(1).
He raises three arguments on appeal. First, he argues the
District Court erroneously denied his motion to suppress
                           2
the firearm recovered by law enforcement. Second, he
argues that the District Court erroneously admitted, under
Federal Rule of Evidence 404(b), evidence that he had
previously obtained guns through a straw purchaser. And
third, he argues that a new trial is warranted because the
District Court permitted the prosecutor to make improper
statements during closing arguments.1 We are not
persuaded by Brown’s argument that evidence of the
firearm should have been suppressed. We agree,
however, that the District Court erred in admitting
evidence of Brown’s past firearm purchases and by
overruling Brown’s objection to the prosecutor’s closing
arguments. Because the Rule 404(b) error was not
harmless, we will vacate the judgment of the District
Court and remand for a new trial.

                             I.

       In the early morning hours of March 23, 2011, four
Pittsburgh Police Detectives—Judd Emery, Mark
Adametz, Calvin Kennedy, and Thomas Gault—were
patrolling Pittsburgh’s Hill District in an unmarked

1
       Brown also argues that 18 U.S.C. § 922(g)(1) is
unconstitutional under the Commerce Clause. Brown
acknowledges that this argument is foreclosed by Third
Circuit precedent, see United States v. Singletary, 268 F.3d
196 (3d Cir. 2001) and United States v. Shambry, 392 F.3d
631 (3d Cir. 2004), and thus raises it for preservation
purposes only.
                             3
police cruiser. As the detectives approached the
intersection of Wylie Avenue and Duff Street, they
observed a 2002 maroon Chevy Impala driven by Ebon
Brown park near the intersection across the street from
the Flamingo Bar, a nuisance bar where drug dealing and
shootings regularly occur. All four detectives believed
the Impala had been parked too close to the intersection
in violation of 75 Pa. Cons. Stat. § 3353. See App. 115,
178, 191, 210.
        The detectives stopped their cruiser in the middle
of the street and watched as Brown and three other
passengers exited the Impala. As Brown was stepping
out, he looked in the detectives’ direction and appeared
to recognize their unmarked cruiser. Brown then sat back
down in the Impala and made a motion which appeared
consistent with removing an object from his waistband
and placing it beneath the driver’s seat. Brown then
stepped out of the vehicle, closed the door, and walked in
the direction of the Flamingo Bar. All four detectives
testified that, based on their experience, they believed
Brown had removed a gun from his person and attempted
to conceal it under the driver’s seat. See App. 117–22,
169, 205, 221–22.

       The detectives exited the police cruiser and
approached Brown and the other passengers. The
detectives’ badges were visible and they identified
themselves as Pittsburgh police officers. Detective Gault
began speaking with Brown and informed him that the
                            4
Impala was parked in an illegal location. As this
exchange was taking place, Detective Emery walked
around to the passenger side of the Impala and shined his
flashlight through the windshield. With the inside of the
vehicle illuminated, Detective Emery observed “the grip
and rear slide portion of a semi-automatic firearm
sticking out from underneath the driver’s seat.” App. 172.
Detective Emery immediately gestured to Detective
Gault (by extending his thumb and index finger) that
there was a gun in the vehicle. After seeing Detective
Emery’s gesture, Detective Gault grabbed Brown to
prevent him from fleeing. The detectives then asked
Brown whether he had a permit to carry the firearm.
When Brown answered that he did not, they placed him
under arrest.

       Detective Emery retrieved the gun from the
Impala, cleared a round from the chamber, and placed it
in the trunk of the detectives’ cruiser. The detectives then
performed pat-down searches of the other passengers, but
found no weapons and did not place anyone else under
arrest. At Brown’s request, the detectives gave the keys
to the Impala to another passenger, James Cole. Cole
moved the Impala to a legal parking space, and then he
and the others proceeded to the Flamingo Bar.

       The Government charged Brown in a single-count
indictment for being a felon in possession of a firearm in
violation of 18 U.S.C. § 922(g)(1). Prior to trial, Brown
filed a motion to suppress the evidence of the gun
                             5
retrieved from underneath the Impala’s seat. He argued
that the police conducted an unlawful Terry2 stop and
that they did not have a lawful basis to search the vehicle.
The District Court denied the motion to suppress, app. 1–
20, and Brown proceeded to trial.
      Brown’s theory at trial was that the firearm
belonged to his girlfriend, Brittney McCoy, and that she
had left it beneath the seat of the Impala without his
knowledge. McCoy testified for the defense and
corroborated Brown’s story. McCoy explained that she
had borrowed the Impala from its owner, Cassandra
Whitaker, on the evening of March 22, 2011, because she
needed it for an appointment the following morning.3
App. 628–29. McCoy stated that immediately after
borrowing the car, she removed the gun—which she had




2
      Terry v. Ohio, 392 U.S. 1 (1968).
3
       Whitaker also testified for the defense and confirmed
that she frequently loaned her car to family members and
friends, including McCoy and Brown, and that she had loaned
the Impala to McCoy on March 22, 2011. App. 581–82.
                             6
purchased for personal protection in August 20094—from
her purse and placed it under the driver’s seat. She then
drove the Impala to Brown’s house and parked it in the
driveway directly behind Brown’s car. According to
McCoy, later that evening while she and Brown were
trying to sleep, her nephew called and asked Brown to
give his girlfriend a ride somewhere. Brown agreed and
left in the Impala (because it was blocking his car in), not
knowing the gun was under the seat. App. 632.
      The Government maintained that Brown
physically possessed the gun and placed it under the seat
of the Impala after he spotted the police cruiser. The
Government also argued that even though McCoy
purchased the gun, she had really purchased it for Brown.
To establish this claim, the Government sought to
introduce under Federal Rule of Evidence 404(b)

4
       McCoy and Whitaker both testified regarding the
events that prompted McCoy to purchase the gun. In August
2009, four armed gunmen broke into Whitaker’s home
looking for money to settle debts owed by McCoy’s brother,
who also happened to be the father of Whitaker’s son.
Whitaker stated that the attackers did not find money in the
home, but stole her television, gun, clothing, jewelry, and car.
They then tied her up and left the house. Whitaker eventually
untied herself and called the police. She then called McCoy to
let her know what had happened and to let her know to be
careful. Fearing for her own safety, McCoy, accompanied by
Whitaker, purchased the gun the following day.
                               7
statements that Brown made nearly seven years earlier in
2005 admitting that he had used a straw purchaser to
acquire firearms. In January 2005, Brown was arrested
by Pittsburgh police for public urination. Pursuant to a
lawful search of Brown’s vehicle in connection with his
arrest, police officers recovered a handgun and more than
250 stamp bags of heroin. After his arrest, Brown agreed
to speak with agents of Pittsburgh’s Bureau of Alcohol,
Tobacco, Firearms, and Explosives (ATFE). Brown
informed ATFE agents that he had repeatedly sold heroin
to a “white male” who had agreed to buy firearms for
Brown in exchange for the drugs. Brown claimed that the
white male had purchased twelve guns on six different
occasions, which Brown then sold to friends and
relatives. Brown was later convicted of possession with
the intent to distribute heroin and possession of a gun in
furtherance of a drug trafficking crime. He was not
charged with any crime related to the straw purchase
transactions.
       In a pretrial motion, Brown sought to exclude the
statement he had made to the ATFE agents about using a
straw purchaser to obtain firearms. In response, the
Government argued the statement was “relevant to show
that [Brown] did have the knowledge that there was a
firearm in his car and that he knows what firearms are.”
App. 388. Further, the Government argued that these
statements supported its theory that McCoy “straw
purchased this firearm for [Brown].” App. 389. Brown
                            8
countered that the statement would be relevant only for
propensity purposes, merely showing that if he had used
straw purchasers before, then he must have used McCoy
as a straw purchaser for this gun. He also argued that the
Government did not have any evidence that McCoy was
involved in the earlier straw purchases or that she
purchased this firearm in concert with Brown. App. 388.

       After hearing from the parties, the District Court
agreed with the Government and concluded that the
evidence was relevant “to show motive or knowledge and
that type of thing along those lines.” App. 390. However,
the Court concluded the statements would be admissible
only if McCoy took the stand and testified that she had
purchased the firearm for personal purposes. App. 388,
431–33, 650–52. The Court also limited the manner in
which the evidence could be introduced, allowing the
Government to introduce only a stipulation that Brown
used straw purchasers to acquire guns. The parties agreed
to the language of a stipulation, which was read to the
jury at the close of evidence. The stipulation provided:
“The      defendant     acknowledges       using    straw
purchasers/third parties to purchase firearms for him in
the past.” App. 683. Despite Brown’s agreement to the
language of the stipulation, the Court noted his
continuing objection to its admissibility under Rule
404(b).

      During summation, defense counsel argued that
there was a gap in the prosecution’s case because there
                            9
was no fingerprint evidence connecting Brown to the
gun. Defense counsel stated that “none of us would have
to be here today if there had been a fingerprint analysis
because it would show what you already know, that Mr.
Brown never possessed that gun or ammunition.” App.
765. At the conclusion of defense counsel’s closing
argument, the prosecution requested an instruction stating
that the Government was not legally obligated to use any
particular investigative technique. App. 779. The Court
agreed and gave the following instruction:

      You have just heard argument by counsel
      that the government did not use specific
      investigative techniques, such as fingerprint
      analysis. You may consider these facts in
      deciding whether the government has met its
      burden of proof . . . . However, there is no
      legal requirement that the government use
      any specific investigative technique . . . .
App. 784.
      The prosecutor then began his rebuttal by flipping
defense counsel’s argument, stating that “[w]e haven’t
heard any expert from the defense” regarding
fingerprints. App. 785. Brown objected to this remark
and argued that it impermissibly placed a burden on the
defense. The Court sustained the objection and struck the
comment. App. 786. The prosecutor then continued to
address the lack of fingerprints. “I want to see if we can
                           10
talk about your own common sense in your daily
experience about fingerprints,” he said. App. 786. The
prosecutor explained that, in the heat of the moment,
detectives do not have time to “get out . . . rubber gloves,
to put this thing in a paper bag, and then go walk it over
to the police vehicle and put it in a plastic evidence bag.”
App. 787. He then followed this point with the following
remarks, which are central to one of Brown’s arguments
on appeal:
             You heard the officer, the first thing
      he did on this particular occasion was to take
      [the gun], he moved the slide back to take
      the one round that was in the chamber out of
      there . . . . And then he extracted the other
      rounds from the magazine . . . . He quickly
      put it back in the police car and in the
      process of doing that, he put his own
      fingerprints on what may have possibly
      existed there. We have no way of knowing
      whether there could be fingerprints on there,
      but I want to talk about your own common
      sense and your daily experiences.

             Many of you probably have children.
      Your children probably touch your coffee
      table. Coffee table may have a glass top to
      it. When you see those marks that are on the
      coffee table from your children, do you see
      fingerprints of the type when the police
                            11
      officers roll fingerprints or do you see
      smudges and smears, things that come into
      contact with that but could not be called
      fingerprints? They’re smudges and smears.
      Even on a nice, clean, smooth surface like a
      piece of glass that is on your coffee table
      you find only smears and smudges, you do
      not find fingerprints.
App. 787–88.
       At this point, defense counsel objected and argued
the prosecution was testifying about facts that were not in
evidence. App. 788 (“You don’t see fingerprints on glass
surfaces. We didn’t hear testimony about that.”). Defense
counsel argued that “the [prosecutor’s] statement fairly
implied, if not explicitly stated, that a fingerprint could
only smudge or smear glass, not put fingerprints on it,
which is — he could suggest that is common sense, that
that’s a fact, but it’s not — we didn’t hear testimony on
that, so we need a qualifier.” App. 789. The District
Court overruled the objection and allowed the prosecutor
to continue making the argument “as long as [he]
direct[ed] [his statements] to common sense and [not the
jurors’] everyday lives.” App. 789.

      After the objection was overruled, the prosecutor
continued arguing that the jurors’ common sense should
inform them that smudges and smears on a glass table
“are not the type of fingerprints that one would roll from
                            12
a police thing.” App. 790. He then extrapolated this point
to the firearm recovered by law enforcement, arguing that
the jurors’ common sense should inform them that a gun
with a “microtextured surface” is equally unlikely to hold
fingerprints. App. 790. (rhetorically asking the jurors: “Is
it likely that you’re going to find fingerprints on [a
firearm with a microtextured surface], from your own
experience, from your common sense . . . ?”).
       The jury returned a verdict convicting Brown of
the single § 922(g)(1) offense charged. The District Court
subsequently sentenced Brown to a 92-month term of
imprisonment. This timely appeal followed.5

                            II.
       Brown raises three arguments on appeal. First, he
contends the District Court erroneously denied his
motion to suppress the firearm. Second, he argues the
stipulation about his prior use of a straw purchaser was
improperly admitted. And third, he argues that a new trial
is warranted because the prosecutor made improper
statements during his closing argument that
fundamentally affected the fairness of the trial. We
address these arguments seriatim.

                            A.

5
       The District Court had jurisdiction under 18 U.S.C. §
3231, and we have jurisdiction under 28 U.S.C § 1291.
                            13
       The Fourth Amendment prohibits “unreasonable
searches and seizures.” U.S. Const. amend. IV. Brown
contends that both his seizure by police and the seizure of
the firearm and ammunition from the Impala were
violative of his Fourth Amendment rights. We disagree.
       Police encounters with citizens fall into one of
three broad categories, each with varying degrees of
constitutional scrutiny: “(1) police-citizen exchanges
involving no coercion or detention; (2) brief seizures or
investigatory detentions; and (3) full-scale arrests.”
United States v. Perez, 443 F.3d 772, 777 (11th Cir.
2006). The first type of encounter does not implicate the
Fourth Amendment. United States v. Williams, 413 F.3d
347, 352 (3d Cir. 2005) (stating that officers do not
violate the Fourth Amendment “merely by approaching
individuals on the street or in other public places”); see
also Florida v. Bostick, 501 U.S. 429, 434 (1991). The
second category (i.e., brief seizures or Terry stops)
requires a showing that the officer acted with reasonable
suspicion. Illinois v. Wardlow, 528 U.S. 119, 123 (2000)
(stating that an officer may “conduct a brief,
investigatory stop when the officer has a reasonable,
articulable suspicion that criminal activity is afoot”)
(citing Terry v. Ohio, 392 U.S. 1, 30 (1968)). And the
third category (i.e., full-scale arrests) is proper only when
an officer has probable cause. Beck v. Ohio, 379 U.S. 89,
91 (1964) (“Whether [an] arrest was constitutionally
valid depends . . . upon whether, at the moment the arrest
                             14
was made, the officers had probable cause to make it.”).
Here, the detectives’ brief interaction with Brown
touched on all three but was valid under each.

      The initial step in our suppression analysis is to
determine whether a seizure has taken place and, if so,
when the seizure occurred. United States v. Torres, 534
F.3d 207, 210 (3d Cir. 2008); Johnson v. Campbell, 332
F.3d 199, 205 (3d Cir. 2003) (stating that in conducting a
suppression analysis, the court “must first determine at
what moment [the defendant] was seized”). As already
noted, a Fourth Amendment seizure “does not occur
simply because a police officer approaches an individual
and asks a few questions.” Bostick, 501 U.S. at 434.
Rather, “[a] seizure occurs only ‘when [a police officer],
by means of physical force or show of authority, has in
some way restrained the liberty of a citizen.’” United
States v. Crandell, 554 F.3d 79, 84 (3d Cir. 2009)
(quoting Terry, 392 U.S. at 19–20 n.16).
       We apply an objective test when evaluating
whether an officer’s “show of authority” would have led
a reasonable person to believe they were not free to
leave. Crandell, 554 F.3d at 84 (stating that the test is
whether a reasonable person in light of all the
circumstances would have perceived the officer’s actions
as restrictive). The Supreme Court has articulated several
factors to be considered as part of this objective inquiry,
including, inter alia, “the threatening presence of several
officers, the display of a weapon by an officer, some
                            15
physical touching of the person of the citizen, or the use
of language or tone of voice indicating that compliance
with the officer’s request might be compelled.” United
States v. Mendenhall, 446 U.S. 544, 554–55 (1980); see
also United States v. Drayton, 536 U.S. 194, 204 (2002).
       Considering these factors, we agree with the
learned District Judge that no seizure occurred prior to
the moment Detective Gault physically grabbed Brown to
prevent him from fleeing the scene. There was nothing
about the detectives’ brief initial approach that
constituted a Fourth Amendment seizure. The evidence at
the suppression hearing shows that the detectives did not
activate their lights or sirens, brandish their weapons,
block Brown’s path, physically touch Brown, or make
any threats or intimidating movements. Instead, the
detectives merely exited their cruiser and approached
Brown in a public space to discuss their concerns about
where the Impala was parked.
        Brown argues that the detectives demonstrated
their authority by approaching in a group of four,
displaying their badges, and identifying themselves as
Pittsburgh police officers. These facts are not enough to
tilt the balance in Brown’s favor. A Fourth Amendment
seizure does not occur merely because police officers
identify themselves when engaging a citizen in
conversation. And although the detectives approached in
a group, as the District Court found, “there was ‘no
threatening presence,’ since the number of detectives
                           16
evenly matched the number of individuals who had
exited the Impala.” App. 11 (citing Mendenhall, 446 U.S.
at 554). We agree with the District Court that the totality
of the circumstances suggests that the detectives’
approach and initial contact with Brown was a mere
encounter that did not implicate the Fourth Amendment.6

       Although the detectives’ initial interaction with
Brown did not implicate the Fourth Amendment, the
encounter ripened into a Terry stop at the moment
Detective Gault grabbed Brown’s waistband to prevent
him from fleeing. Although this conduct constituted a
Fourth Amendment seizure, it is well-established that
officers do not need to obtain a warrant to “conduct a
brief, investigatory stop when the officer has a
reasonable, articulable suspicion that criminal activity is

6
       Brown also argues that the detectives made a “show of
authority” by taking action that was “more aggressive than
necessary.” Appellant’s Br. at 28. More specifically, he
argues that if the detectives “were concerned about the safety
of the Impala’s position, they should have rolled down their
windows and asked that it be moved” rather than approaching
on foot. This argument misses the point. The question is not
what course of conduct the detectives “should” have pursued,
but whether their actions were constitutionally permissible.
As already explained, the brief initial encounter did not
constitute a Fourth Amendment seizure. The simple fact that
the detectives could have taken another course of action does
not render their conduct unconstitutional.
                             17
afoot.” Wardlow, 528 U.S. at 123 (citing Terry, 392 U.S.
at 30).

        Reasonable suspicion is “a less demanding
standard than probable cause and requires a showing
considerably less than preponderance of the evidence.”
Wardlow, 528 U.S. at 123 (citing United States v.
Sokolow, 490 U.S. 1, 7 (1989)). The officer must simply
have some objective justification for the stop and must be
able to articulate more than an “unparticularized
suspicion or ‘hunch’” that the suspect is engaged in
criminal activity. Wardlow, 528 U.S. at 124 (citing Terry,
392 U.S. at 27). When making reasonable suspicion
determinations, reviewing courts “must look at the
‘totality of the circumstances’ of each case to see whether
the detaining officer has a ‘particularized and objective
basis’ for suspecting legal wrongdoing.” United States v.
Arvizu, 534 U.S. 266, 273 (2002) (quoting United States
v. Cortez, 449 U.S. 411, 417 (1981)). “This process
allows officers to draw on their own experience and
specialized training to make inferences from and
deductions about the cumulative information available to
them that ‘might well elude an untrained person.’” Id.
(quoting Cortez, 449 U.S. at 418). We “give considerable
deference to police officers’ determinations of reasonable
suspicion.” United States v. Mosley, 454 F.3d 249, 252
(3d Cir. 2006)

      We agree with the District Court that Detective
Gault’s brief seizure of Brown was supported by
                            18
reasonable suspicion. Detective Gault grabbed Brown
after Detective Emery had legally observed the firearm
under the Impala’s driver’s seat and communicated his
discovery by making a hand gesture. Although there may
be some circumstances where simple knowledge of a
firearm does not provide reasonable suspicion for a Terry
stop, see United States v. Ubiles, 224 F.3d 213, 218 (3d
Cir. 2000), here the observation of the firearm is
considered in conjunction with the fact that the officers
witnessed Brown make furtive movements consistent
with an attempt to conceal the weapon and the fact that
the encounter occurred in a “high crime area.” Wardlow,
528 U.S. at 124; see id. (“[O]fficers are not required to
ignore the relevant characteristics of a location in
determining whether the circumstances are sufficiently
suspicious to warrant further investigation.”); United
States v. Valentine, 232 F.3d 350, 356 (3d Cir. 2000)
(noting the fact that the stop occurred in a “high crime
area” among the relevant contextual considerations in a
Terry analysis). Viewing these circumstances as a whole,
we find that the brief detention of Brown was justified by
reasonable suspicion.

      We also find no constitutional infirmity with
Brown’s subsequent custodial arrest. Immediately after
seizing Brown, the detectives inquired whether he had a
permit to carry the firearm. When Brown answered that
he did not, the officers placed him under arrest. Brown’s
admission that he lacked a permit to carry the firearm
                           19
provided probable cause to support his arrest.
       The detectives also did not violate the Fourth
Amendment when they recovered the gun from the
Impala. Officers may conduct a warrantless search of a
vehicle incident to arrest in two instances: “(1) if the
arrestee is within reaching distances of the vehicle during
the search, or (2) if the police have reason to believe that
the vehicle contains ‘evidence relevant to the crime of
arrest.’” Davis v. United States, 131 S. Ct. 2419, 2425
(2011) (quoting Arizona v. Gant, 332 U.S. 332, 344
(2009)). This case fits squarely within the second
exception because unlawful firearm possession was the
crime for which Brown was arrested.
       For these reasons, we will affirm the District
Court’s denial of Brown’s motion to suppress the
firearm.

                            B.

       Brown next challenges the District Court’s
decision to allow the Government to introduce evidence
that he had previously used a straw purchaser to obtain
firearms. We hold that the admission of this evidence
was improper.
       Federal Rule of Evidence 404(b), which governs
the admissibility of a defendant’s prior bad acts, provides
that “[e]vidence of a crime, wrong, or other act is not

                            20
admissible to prove a person’s character in order to show
that on a particular occasion the person acted in
accordance with the character.” Fed. R. Evid. 404(b)(1).
The rule states, however, that “[t]his evidence may be
admissible for another purpose, such as proving motive,
opportunity, intent, preparation, plan, knowledge,
identity, absence of mistake, or lack of accident.” Fed. R.
Evid. 404(b)(2).
       We have explained that Rule 404(b) is generally a
rule of exclusion. United States v. Caldwell, — F.3d —,
2014 WL 3674684, at *5 (3d Cir. July 24, 2014). It
“directs that evidence of prior bad acts be excluded—
unless the proponent can demonstrate that the evidence is
admissible for a non propensity purpose.” Id. Our
opinions have repeatedly and consistently emphasized
that the party seeking to admit evidence under Rule
404(b)(2) bears the burden of demonstrating its
applicability. Id. at *6.
       There are four distinct steps that must be satisfied
before prior bad act evidence may be introduced at trial:
(1) it must be offered for a proper non-propensity
purpose that is at issue in the case; (2) it must be relevant
to that purpose; (3) its probative value must not be
outweighed by the danger of unfair prejudice under Rule
403; and (4) it must be accompanied by a limiting
instruction, if one is requested. Caldwell, 2014 WL
3674684, at *7 (citing United States v. Davis, 726 F.3d
434, 441 (3d Cir. 2013)). This methodical process
                             21
requires “careful precision” by both the proponent in
proffering the prior act evidence and by the trial judge
who must decide the question of admissibility. Id. at *4.

      At trial, the Government argued that Brown’s 2005
statement to ATFE agents that he had used a straw
purchaser to obtain firearms was “relevant to show that
he did have the knowledge that there was a firearm in his
car and that he knows what firearms are.” App. 388.
Applying the framework described above, we must first
determine whether the identified non-propensity purpose
(here, “knowledge”) is at issue in the case, and then
evaluate whether the evidence is relevant to that purpose.

       When evaluating whether a non-propensity
purpose is at issue, we “consider the ‘material issues and
facts the government must prove to obtain a conviction.’”
Caldwell, 2014 WL 3674684, at *6 (quoting United
States v. Sampson, 980 F.2d 883, 888 (3d Cir. 1992)). In
other words, the government cannot offer Rule 404(b)
evidence for a non-propensity purpose if doing so would
not materially advance the prosecution’s case. Here,
Brown was charged with unlawful possession of a
firearm by a convicted felon, 18 U.S.C. § 922(g)(1),
which requires proof that: “(1) the defendant has been
convicted of a crime of imprisonment for a term in
excess of one year; (2) the defendant knowingly
possessed the firearm; and (3) the firearm traveled in
interstate commerce.” United States v. Huet, 665 F.3d
588, 596 (3d Cir. 2012). Thus, the Government may
                           22
introduce Rule 404(b) evidence only if it is offered for a
non-propensity purpose that is probative of one of the
elements essential for a conviction.

       We reject out of hand the Government’s argument
that the evidence was admissible to show that Brown
“knows what firearms are.” App. 388. It is conceivable
that a defendant might challenge a § 922(g)(1) charge by
claiming he does not know what a firearm is.7 In the
ordinary course, however, a defendant’s general
knowledge about firearms is not in question in a felon-in-
possession case, and the government is thus not required
to show that the defendant “knows what firearms are” to
secure a conviction. To be sure, Brown did not claim he
was unfamiliar with firearms. Absent such a claim or
suggestion by a defendant, a rule permitting the
introduction of Rule 404(b) evidence for the purpose of
showing the defendant “knows what firearms are” would
have the effect of rendering all prior bad acts related to

7
        Unlike a drug case, where the unfamiliar nature of the
substance may allow a defendant to claim he mistook the substance
for something else or otherwise did not know he possessed drugs,
see, e.g., United States v. Long, 225 F.3d 656 (4th Cir. 2000) (per
curiam) (defendant claiming he did not know the substance at issue
was cocaine, but believed it to be a hormone stimulant to help
chickens become better fighters), it is difficult to imagine a
scenario where a defendant could contend he did not know the
object in his possession was a firearm. Indeed, we have been
unable to find any case where a defendant has made such a
defense.
                                 23
firearms admissible in a felon-in-possession trial. Such a
result could not have been the intent of the drafters of the
Federal Rules of Evidence.

       We thus turn to whether the evidence was
admissible to show Brown “had knowledge there was a
firearm in his car.” App. 388. We have recently
explained that a defendant’s knowledge is rarely at issue
in a weapons-possession case when the prosecution relies
exclusively on a theory of actual possession. Caldwell,
2014 WL 3674684, at *8. This is because, “absent
unusual circumstances . . . , the knowledge element in a
felon-in-possession case will necessarily be satisfied if
the jury finds the defendant physically possessed the
firearm.” Id. In contrast, however, “[e]vidence of
knowledge . . . is critical in constructive possession cases,
as ‘[a] defendant will often deny any knowledge of a
thing found in an area that is placed under his control
(e.g., a residence, an automobile) or claim that it was
placed there by accident or mistake.’” United States v.
Williams, 620 F.3d 483, 489 (5th Cir. 2010) (quoting
United States v. Jones, 484 F.3d 783, 788 (5th Cir.
2007)). This case presents the “paradigmatic constructive
possession scenario,” United States v. Garner, 396 F.3d
438, 443 (D.C. Cir. 2005), where a firearm is found in
proximity to a defendant who claims he did not know it
was there. Accordingly, we have no difficulty concluding
that showing Brown’s knowledge that the gun was in the
Impala was an appropriate non-propensity purpose for
                             24
offering the evidence of Brown’s previous straw
purchases.

       Yet it is not enough for the Government to merely
identify a valid non-propensity purpose under Rule
404(b)(2). Crucially, the Government must also show
that the evidence is relevant to that purpose. To do so, the
prosecution “must clearly articulate how that evidence
fits into a chain of logical inferences, no link of which
can be the inference that because the defendant
committed [the proffered prior offense], he therefore is
more likely to have committed [the charged offense].”
Sampson, 980 F.2d at 887. This is where the
Government’s proffer falls short. The Government has
completely failed to explain how the fact that Brown
used a straw man in 2005 to purchase firearms tends to
prove that he knowingly possessed the gun under the
driver’s seat of the Impala six years later. These are two
entirely distinct acts, and participation in one has no
relationship to the other. See Davis, 726 F.3d at 443
(holding that defendant’s prior conviction for cocaine
possession not admissible to show knowledge in a trial
for cocaine distribution because “[p]ossession and
distribution are different in ways that matter”); cf.
Caldwell, 2014 WL 3674684, at *12 (“If the prior
possession was of a different gun, then its value as direct
or circumstantial evidence of the charged possession
drops and the likelihood that it is being used to show
propensity to possess guns rises considerably. Similarly,
                            25
as the prior possession is further removed in time, it
becomes less probative of possession on the date
charged.”) (citation omitted).

       The Government’s primary argument, which was
accepted by the District Court, is that the straw purchaser
evidence refutes McCoy’s testimony that she purchased
the gun for her own personal protection. According to the
Government, the fact that Brown used a straw purchaser
in the past makes it more likely that he used McCoy as a
straw purchaser to obtain the gun recovered by the
detectives. Extrapolating from this proposition, the
Government argues then that it is likely that Brown knew
about the gun in Whitaker’s Impala. There are multiple
problems with this line of reasoning.
       First, the fact that Brown used a straw purchaser to
obtain firearms in 2005 does not discredit McCoy’s
testimony that she purchased the gun for personal
protection in August 2009. The circumstances
surrounding Brown’s use of a straw purchaser were
unique to him—he was selling heroin to an unnamed
individual who agreed to purchase firearms in exchange
for drugs. There is no parallel between that scenario and
McCoy’s purchase of the firearm in August 2009, one
day after four armed men assaulted her friend in an
attempt to collect debts owed by her brother. The
Government did not present evidence disputing the
sequence of events surrounding McCoy’s purchase of the
firearm. An even more conspicuous omission was its
                            26
failure to present evidence that McCoy had previously
participated in a straw purchase with Brown (or anyone
else for that matter). And significantly, this all occurred
while Brown was still serving a prison sentence for his
2005 conviction. It is simply too great a leap in logic to
suggest that because Brown once used a straw purchaser
in a quid pro quo drug transaction, he must also have
used McCoy as a straw purchaser for the gun recovered
in Whitaker’s Impala. And it is an even greater leap to
then conclude that such a strained inference somehow
made it more likely than not that Brown constructively
possessed the firearm.

       All of this aside, there is an even more
fundamental problem with the Government’s proffer
under Rule 404(b). Quite simply, the Government’s chain
of inferences is indubitably forged with an impermissible
propensity link. The first logical step in the
Government’s analysis requires the jury to conclude that
because Brown used a straw purchaser in the past, he
must therefore have used a straw purchaser here. This is
propensity evidence, plain and simple. Davis, 726 F.3d
at 442 (“[T]he government must explain how [the
evidence] fits into a chain of inferences—a chain that
connects the evidence to a proper purpose, no link of
which is a forbidden propensity inference.”).
       Our concern that the evidence went only to show
Brown’s propensity to commit gun crimes is not
alleviated by the District Court’s explanation for why the
                            27
evidence was admitted. As we have explained, “[t]he
district court, if it admits the evidence, must in the first
instance, rather than the appellate court in retrospect,
articulate reasons why the evidence also goes to show
something other than character.” Sampson, 980 F.2d at
888; see also Caldwell, 2014 WL 3674684, at *7 (“[O]ur
decisions are . . . emphatic in requiring the proponent and
the trial judge to articulate, with precision, a chain of
inferences that does not contain a propensity link.”)
(emphasis added). After hearing from the parties, the
Court concluded that the prosecution could “use this
[evidence] to show motive or knowledge and that type of
thing along those lines.” App. 390 (emphasis added).
This statement does not reflect the type of “careful
precision” our precedent demands. Caldwell, 2014 WL
3674684, at *4. It supplies the defendant with little notice
of the non-propensity purpose for which the evidence
against him is being admitted, and it says nothing of how
the evidence is probative of that purpose. Of course, “a
mere recitation of the purposes in Rule 404(b)(2) is
insufficient.” Davis, 726 F.3d at 442; see also
Christopher B. Mueller & Laird C. Kirkpatrick, Federal
Evidence § 4:28, at 730 (“[I]t is lamentably common to
see recitations of laundry lists of permissive uses, with
little analysis or attention to the particulars.”).
      When confronted with a proffer under Rule 404(b),
a district court should not merely inquire of the
prosecution what it wishes the evidence to prove. Rather,
                            28
the court should also require the prosecution “to explain
‘exactly how the proffered evidence should work in the
mind of a juror to establish the fact the government
claims to be trying to prove.’” Caldwell, 2014 WL
3674684, at *12 (quoting United States v. Miller, 673
F.3d 688, 699 (7th Cir. 2012)) (emphasis added). In our
case, that means the District Court should have asked the
Government to answer this question: “How, exactly, does
Brown’s admission to ATFE agents that he sold heroin in
exchange for firearms in 2005 suggest that he had
knowledge of the gun found under the driver’s seat of the
Impala on the morning of March, 23, 2011?” Put to this
task, the Government would have been unable to
articulate the requisite chain of inferences without resort
to propensity-based links or attempts to build a bridge too
far.8


8
       The Government has modified and expanded its
position on appeal. It now argues that the evidence of past
straw purchases is relevant to show not only that Brown knew
the gun was in the Impala, but also that he “knew how to
obtain a gun through the use of a straw purchaser, had the
intent to possess the firearm, and his possession was not
unknowing, accidental or mistaken.” Gov’t Br. at 41. Setting
aside that these arguments were not advanced in its proffer
before the District Court, the Government has still not shown
that these are proper grounds for admission. The material
issue in the case was whether Brown knew the gun was under
the driver’s seat of the Impala, not whether he knew how to
                             29
       For these reasons, we conclude that the evidence
that Brown used a straw purchaser to obtain firearms in
the past was admitted in error. Nevertheless, the
Government maintains that, even if erroneous, the
admission of evidence regarding Brown’s past use of a
straw purchaser was harmless. “The test for harmless
error is whether it is ‘highly probable that the error did
not contribute to the judgment.’” United States v.
Cunningham, 694 F.3d 372, 391–92 (3d Cir. 2012)
(citation omitted). We will find such a high probability
only when we have a “sure conviction” that the error did
not unfairly prejudice the defendant. Id. at 392.

       The Government contends the error was harmless
because the evidence of Brown’s past involvement with a
straw purchaser was introduced only by way of a brief
stipulation that did not discuss the specific details of the
prior act. We are not persuaded by this argument.
Whether offered in a brief stipulation or a simple “yes”
or “no” question on cross-examination, the prejudicial
impact of prior bad act evidence is significant. As the
Supreme Court has explained, when—as here—proffered
prior bad act evidence serves only to show the

obtain firearms through straw purchasers. And for the same
reasons set forth above, it is too great a leap to suggest that
the fact that Brown used a straw purchaser to obtain guns
seven years ago tends to prove his intent to possess the gun
that is the subject of this charged crime.

                              30
defendant’s propensity to act unlawfully, “it is said to
weigh too much with the jury and to so overpersuade
them as to prejudge one with a bad general record and
deny him a fair opportunity to defend against a particular
charge.” Michelson v. United States, 335 U.S. 469, 476
(1948)). See also Fed. R. Evid. 404(a) Advisory
Committee’s Note (“Character evidence is of slight
probative value and may be very prejudicial. It tends to
distract the trier of fact from the main question of what
actually happened on the particular occasion. It subtly
permits the trier of fact to reward the good man and to
punish the bad man because of their respective characters
despite what the evidence in the case shows actually
happened.”). In this case, the stipulation suggested to the
jury that Brown was a bad actor with a history of gun
crimes. This necessarily impugns his character and tends
to impermissibly sway the balance in the Government’s
favor. To hold the error harmless merely because the
evidence was offered by way of stipulation would create
a blueprint for introducing improper Rule 404(b)
evidence in a manner insulated from the consequences of
appellate review. We decline to endorse such a rule.

      The Government also argues the error was
harmless because the remainder of the Government’s
evidence that Brown knowingly possessed the gun was
“overwhelming.” Gov’t Br. at 51. There is no doubt that
the Government presented a substantial case against
Brown, including offering consistent testimony from all
                            31
four detectives that he made furtive movements
consistent with concealing a firearm under the driver’s
seat of the Impala. At the same time, however, the
Government failed to present anyone who could put the
firearm in Brown’s hands. And Brown introduced his
own witness, McCoy, who testified that she placed the
gun under the seat without Brown’s knowledge. In the
end, it may well be that the jury would have convicted
Brown with or without the straw purchaser stipulation.
Nonetheless, there is not enough on this record for us to
possess a “sure conviction” that this is so. We therefore
must conclude the error was not harmless.

                            C.
       Because we conclude that the erroneous admission
of Rule 404(b) evidence was not harmless error, we are
not required to address Brown’s final contention that the
District Court erred by not sustaining his objection
during the prosecutor’s rebuttal summation. However, in
the interest of providing guidance to the District Court on
remand, we will briefly explain why the prosecutor’s
remarks during rebuttal were improper.
        Brown argues that the prosecutor improperly
testified about facts not in evidence when he suggested
(1) that Brown’s fingerprints were covered up by the
detective who retrieved the gun from the Impala, and (2)
that fingerprints could not be recovered from smooth
surfaces like a glass table or the exterior of a gun. We
                            32
agree with Brown’s argument.
       Improper statements made during summation may
warrant a new trial when such statements “cause[] the
defendant substantial prejudice by so infecting the trial
with unfairness as to make the resulting conviction a
denial of due process.” United States v. Shareef, 190 F.3d
71, 78 (2d Cir. 1999) (internal quotation marks and
citations omitted). Our first task is to determine whether
the prosecutor’s comments were improper. United States
v. Mastrangelo, 172 F.3d 288, 297 (3d Cir. 1999). “If we
conclude that a comment was improper, we must apply a
harmless error analysis, looking to see if ‘it is highly
probable that the error did not contribute to the
judgment.’” Id. (quoting United States v. Zehrbach, 47
F.3d 1252, 1265 (3d Cir. 1995) (en banc)).

       During closing arguments, a criminal defendant
“certainly is entitled to direct the jury’s attention to what
he believes are loopholes in the government’s case and to
argue that these loopholes establish the non-existence of
facts which the government would have proven if it had
the evidence.” United States v. Rubinson, 543 F.2d 951,
965–66 (2d Cir. 1976). Rebuttal summation provides the
Government an opportunity to respond to those
arguments. “As a general rule, Government counsel
should not be allowed to develop new arguments on
rebuttal, but should be restricted to answering the
arguments put forth by defense counsel.” United States v.
Taylor, 728 F.2d 930, 936 (7th Cir. 1984) (citations
                             33
omitted). “While the prosecution in rebuttal may explain
why it has not proven certain facts or respond to the
interpretation which the defense has placed on its failure
to present evidence, it may not use the defense’s
comments to justify the reference to facts or the assertion
of claims which it could have, but did not, introduce at
trial.” Rubinson, 543 F.2d at 966; see also United States
v. Gray, 876 F.2d 1411, 1417 (9th Cir. 1989) (“[I]t is
improper to base closing arguments upon evidence not in
the record.”); Charles Alan Wright et. al, Federal
Practice and Procedure § 588 (4th ed. 2011) (“It is
misconduct for a prosecutor to make an assertion to the
jury of a fact, either by way of argument or by an
assumption in a question, unless there is evidence of that
fact.”).

       We conclude that the prosecutor’s argument that
fingerprints could not have been extracted from the
firearm inappropriately relied on facts not in evidence.
During his closing, defense counsel questioned the
Government’s proof by pointing out the lack of forensic
fingerprint evidence. It would have been permissible for
the prosecution to respond to this argument by noting the
general challenges police officers face in trying to
preserve forensic evidence in the rapidly-unfolding
events surrounding an arrest. It was not appropriate,
however, to suggest or speculate that the particular
firearm at issue was incapable of retaining identifiable
fingerprints—at least not without evidence to substantiate
                            34
that claim. The Government could have presented expert
testimony to explain that the surface of the firearm at
issue would not hold fingerprints, or that the detectives
covered up any identifiable prints when they removed the
gun from the Impala. Failing to do so, however, the
Government was not permitted to make this argument
during its rebuttal summation. In short, the prosecutor
was testifying.
        The Government contends that the prosecutor was
merely asking the jurors to use their own common sense
and attempting to draw upon their “ordinary experiences
concerning when fingerprint evidence would be
recoverable.” Gov’t Br. at 58. We seriously doubt that
jurors possess a common understanding of the
circumstances under which investigators can extract
fingerprints from a weapon, a glass table, or any other
surface. A juror may have observed a smudge on her
coffee table, but that does not translate into an
understanding of when such a smudge can be extracted
by law enforcement as an identifiable fingerprint.9 Nor
does it provide the juror with a “common sense”
understanding about whether the “microtextured surface”
of a firearm will hold fingerprints. App. 790.

      To be sure, the Government was not legally

9
        Indeed, the District Court even challenged the
prosecutor’s suggestion, stating “You can get fingerprints off
glass, if it’s done right.” App. 789.
                             35
obligated to conduct a fingerprint analysis of the firearm
in the Impala. Nor was it required to offer a forensic
expert at trial in order to carry its burden of proof.
Indeed, at the Government’s request, the jury was
instructed that “there is no legal requirement that the
government use any specific investigative technique” in
order to establish Brown’s culpability. App. 784. Yet by
electing not to present such evidence explaining its
inability to obtain fingerprints from the firearm, the
Government could hardly then argue that issue to the
jury. We conclude the prosecutor’s remarks were
improper.10

                            III.
       For the reasons set forth above, we will vacate the
judgment of the District Court and will remand for a new
trial.




10
       In the ordinary course, we would now turn to consider
under a harmless error analysis whether the improper
comments were so prejudicial that a new trial is warranted.
See Mastrangelo, 172 F.3d at 297 (“If we conclude that a
comment was improper, we must apply a harmless error
analysis . . . .”). However, such analysis is not necessary
because we have already concluded Brown’s conviction must
be vacated on other grounds.
                            36
SHWARTZ, Circuit Judge, concurring in part and dissenting
in part.

       I agree with my colleagues that the District Court
properly denied the motion to suppress and that the
Government’s comments in its rebuttal summation
concerning fingerprint evidence were improper. We part
company, however, because even if the evidence of Brown’s
use of straw purchasers was improperly admitted,1 I would
nonetheless conclude that the error was harmless. Thus, I
respectfully concur in part and dissent in part.

       1
         Because I believe that any error in admitting the prior
bad act evidence was harmless, I would not reach the closer
question of whether admission of the evidence violates Fed.
R. Evid. 404(b). I note, however, that Rule 404(b)(2) does
not bar all evidence that could also lead to an inference of
propensity. If it did, then the cautionary instruction that trial
courts must deliver upon request under Huddleston v. United
States, 485 U.S. 681, 691-92 (1988), to ensure that that the
evidence is not used for an improper propensity purpose
would be unnecessary. In this case, even though the evidence
could demonstrate a propensity for using others to buy guns
for Brown, I believe the evidence had a proper purpose under
Rule 404(b)(2)—namely, to refute Brown’s defense that his
girlfriend purchased the gun for herself and that he did not
know she left it in the car, and thereby show Brown knew of
the gun’s presence in the car and that it was not there by
mistake. Cf. United States v. Moorehead, 57 F.3d 875, 878
(9th Cir. 1995) (permissible admitting testimony that a
witness observed the defendant with the same gun in the past
to rebut a defense witness’s claim that she placed the gun
under the seat).




                               1
       This Court has held that “[w]here evidence is
improperly admitted, reversal is not required where it is
highly probable that the error did not contribute to the
judgment.” United States v. Berrios, 676 F.3d 118, 131 (3d
Cir. 2012) (quotation marks omitted); United States v.
Cunningham, 694 F.3d 372, 392 (3d Cir. 2012) (an error is
deemed harmless unless the Court has a “sure conviction that
the error did not prejudice the defendant” (quotation marks
omitted)). When measured against the evidence presented, I
would conclude that it is highly probable that any error did
not contribute to the judgment.

        First, four detectives testified that they saw Brown in
his car, reach in the area of his waistband, and then move in a
way consistent with reaching under his seat. Second, the gun
was found partly tucked under that seat. While the gun may
not have been seen in Brown’s hand, Maj. Op. at 29, it was
precisely where the detectives saw him reach. Third, the gun
was visible to those outside of the car and hence was very
likely visible to one seated inside it. Fourth, the prior bad act
evidence, which involved conduct different from the conduct
charged, was admitted in a short statement and offered in a
very sanitized way.2 The jury was not exposed to any of the
details that the Majority describes regarding Brown’s
statement to the Bureau of Alcohol, Tobacco, Firearms, and
Explosives about his arrangement to use one of his drug

       2
        I agree with my colleagues that packaging evidence
in a stipulation does not immunize it from the careful
weighing that we require under Fed. R. Evid. 403, but we
should nonetheless examine how the evidence was presented,
used, and compared with the other evidence offered when
conducting a harmless error analysis.




                                2
customers to buy him guns in exchange for drugs. Rather, the
jury was told only that “the defendant acknowledges using
straw purchasers/third parties to purchase firearms for him in
the past.” App. 683. Fifth, the limited evidence that the jury
heard was presented only because of, and to refute, Brown’s
defense3 and it was not harped on, as it was mentioned only
once during closing argument. Cf. United States v. Smith
725 F.3d 340, 344 (3d Cir. 2013) (noting that the Government
repeatedly referred to the defendant’s prior bad acts in
summation). Thus, the evidence in this constructive
possession case was strong and it is highly probable that the
single reference to Brown’s prior use of others to purchase
firearms for him did not contribute to the judgment. As the
prior bad act evidence did not prejudice Brown, the admission
of the evidence was harmless and I would therefore affirm the
judgment.4

        Accordingly, I respectfully concur in part and dissent
in part.




       3
          Furthermore, the prior use of straw purchasers was
not the Government’s only method of impeaching Brown’s
girlfriend. On cross-examination, the Government elicited
that she had not been truthful about her employment on her
gun permit, she was not familiar with guns, and she had told
Brown’s probation officer she did not own a gun.
        4
           The Government’s improper comments during
summation do not change the result, in light of the strong
evidence of Brown’s guilt and the District Court’s nearly
contemporaneous instruction that the summations were
merely argument that the jury could not treat as evidence.




                               3
