In an October manslaughter trial in Philadelphia, the jury heard a lot about the victim, information not limited to conduct at the time of the fight that led to his death. The jury heard, as an early defense witness, from a bartender from Florida. Although the death occurred in 2018, the jury heard about an incident in 2008, a decade earlier. As reported by the Philadelphia Inquirer, here is what was testified to:

"Defense attorneys on Friday called Philip Birchfield to the stand. Birchfield, of Destin, Florida, testified that he encountered [victim] in 2008 while working as a security guard at a bar in the coastal Florida city. Birchfield said other bouncers tried to eject [victim], but he became so unruly it took three of them to carry [victim] outside. Birchfield said [victim] threw punches during the encounter and eventually bit Birchfield's elbow, leaving a scar that remains."

"He was just going wild," Birchfield said.

The Rittenhouse stabbing trial doesn't answer a key question: What provoked the fatal confrontation?

The testimony—putting aside the concern over remoteness—is permissible in Pennsylvania. The commonwealth's evidence rules specifically allow proof of acts—whether there was a conviction, the act was charged criminally or the incident as just alleged. Why? Pennsylvania Rule of Evidence 405(b)(2) specifically allows this: "In a criminal case, when character or a character trait of an alleged victim is admissible under Pa.R.E. 404(a)(2)(B) the defendant may prove the character or character trait by specific instances of conduct."

But would it be allowed in federal trials? The answer is "not as in the Pennsylvania prosecution, but maybe sometimes."

At first blush, the answer is a resounding "no" because the Federal Rules of Evidence allow character to be proved only by opinion or reputation, except when character is an element of a claim, charge or defense, a circumstance that almost never arises). Character is not an element of self-defense; but character might prove whether the victim was the initial aggressor or escalated the encounter. Again, though, it would be proved by calling witnesses to say "It is my opinion that the victim was aggressive/violent" or "everyone says the victim was aggressive/violent."

Case law makes this clear, see United States v. Gulley, 526 F.3d 809, 819 (5th Cir. 2008) (finding such evidence to be inadmissible); United States v. Gregg, 451 F.3d 930, 935 (8th Cir. 2006) (noting "specific acts evidence is not admissible to prove a victim acted in conformity with his character" under the federal rules); and United States v. Keiser, 57 F.3d 847, 857 (9th Cir. 1995) (excluding such evidence because "the victim's violent nature is not essential to a successful claim of self-defense").

Nonetheless, there is one clear exception to this ban, and possibly a second one. The clear exception is when the defendant/accused knew/heard of the violent act(s) of the victim; that knowledge is relevant to the fear and perception of danger the accused had, and that fear may make the conduct justified or at least without malice.

Again, case law confirms this in United States v. Saenz, 179 F.3d 686, 688–89 (9th Cir. 1999) (finding that Rule 404(b) does not bar the admissibility of evidence of the defendant's knowledge of a victim's prior bad acts as probative of the defendant's fearful mental state); Government of Virgin Islands v. Carino, 631 F.2d 226, 229 (3d Cir. 1980) (finding that evidence of a victim's prior conviction, which the defendant had knowledge of, is admissible under 404(b) as probative of the defendant's state of mind); in United States v. Gregg, 451 F.3d at 935 (citing Saenz and noting that "evidence of specific instances of a victim's prior violent conduct for purposes of proving a defendant's state of mind" is admissible "to the extent a defendant establishes knowledge of such prior violent conduct at the time of the conduct underlying the offense charged."): and in United States v. Castillo, (D.N.M. Sept. 23, 2010) (accepting the reasoning of the circuit courts and finding evidence of the victim's prior conduct admissible under 404(b) to show the defendant's state of mind).

And the other possible exception? A due process "right to present a defense" claim. One court has so held. But to appreciate it, one must appreciate the context (a murder where the defendant shot and killed a man on his—the defendant's—porch). The other act proof is described below in Fortini v. Murphy, 257 F.3d 39, 42-43 (1st Cir. 2001):

"According to witnesses, shortly before Monterio arrived at Fortini's house, Monterio ran onto a basketball court where four white males were playing night basketball. Monterio then struck, or attempted to strike, all four men. After his companion (Lopes) pulled him away, Monterio yelled, "I'll kill them all. Remember my face, I'm Ceasar Monterio. I'm the baddest motherfucker in town." Immediately after the confrontation, Monterio and Lopes walked toward Fortini's house. On the way, a police officer heard Monterio again yell, "I'm bad. I'm the baddest motherfucker in the world." Monterio arrived at Fortini's house a few minutes later. In his pretrial motion, Fortini argued that the evidence of this episode was admissible because the fight and the shooting had a "temporal and schematic nexus," and that the evidence—by showing that Monterio had been violent that night and was acting in "hot blood"—supported in various ways Fortini's claim of self defense.

In considering the conviction on federal habeas review, the U.S. Court of Appeals for the First Circuit opined that the proof "should have been admitted under conventional evidence rules …" but also put a constitutional gloss on it, discussing whether exclusion might be so destructive to the core defense as to violate due process, a conclusion the First Circuit declined to reach.

Stretching Fortini, a Colorado district court judge misread it as holding that "the First Circuit held that prior violence by the victim, even though unknown to the defendant, was relevant under Rule 404 as tending to portray the victim as a violent man …"see United States v. Sablan, 2008 U.S. Dist. LEXIS 23537, *41, 75 Fed. R. Evid. Serv. (Callaghan) 1187.

That is decidedly not what the First Circuit held, and in Fortini the other act occurred within minutes of the murder, arguably making it part of the course of events and directly reflective of the victim's emotional state in that moment. So Sablan is the outlier.

And the meaning? Unless the defendant knew of the other acts or the conduct was in the same stream of events, federal trials will not proceed as the Philadelphia case did. For better or worse, where one is tried will determine when prior act proof is admissible to show propensity.

—The author thanks Philadelphia attorney and evidence professor Shanin Specter and his teaching assistant Brianna Messina at the University of Pennsylvania Law School, who shared their legal research on this issue.

Jules Epstein is professor of law and director of advocacy programs at Temple University Beasley School of Law.