Imagine that after years of meticulous research, a team of doctors, scientists, and criminologists publish a study of convicted murderers. The team has concluded that the vast majority of murderers have certain traits in common. They include personality traits--such as aggression, and environmental traits--such as access to a weapon, and abusive parents. The team of experts further declares that these traits so frequently reoccur among convicted murderers, they can predict with confidence that an aggressive person with access to a weapon and abusive parents is significantly more likely to murder than the rest of the population. The study receives universal acclaim within the scientific community and is immediately included in every respected treatise on the subject. Prosecutors throughout the country are eager to bring a homicide case to trial and try out the new "Convicted Murderer Profile." Trial judges, meanwhile, struggle with the question: to what extent should this evidence be admissible against a defendant who "fits the profile"?
Profile and syndrome evidence shows a correlation between certain traits or characteristics and particular forms of behavior. (1) After compiling data from numerous cases, experts then attempt to "construct a diagnostic or predictive 'profile' for such behavior." (2) Profile and syndrome evidence invites the inference that individuals who fit a profile or possess a syndrome are likely to have acted in a certain way.
Courts differ greatly in their attempts to define whether profile and syndrome evidence should be admissible, and if so, under what theory of evidence. (3) The Federal Rules of Evidence liberally admit any relevant evidence, unless the Constitution, a statute, or a different rule directs otherwise. (4) "Evidence is relevant if it has any tendency to make a fact more or less probable than it would be without the evidence." (5) Intuitively, most people would likely accept a "Convicted Murderer Profile" as at least moderately predictive of behavior, satisfying the "any tendency" standard of Rule 401. Furthermore, the universal recognition in the scientific community of the Profile would satisfy Federal Rules 702 (6) and 703, (7) governing expert testimony. Meeting these standards, the majority of jurisdictions today would conclude by examining the evidence under Rule 403, (8) and admit the "Convicted Murderer Profile" if the court determined that the probative value of the evidence was not substantially outweighed by the danger of unfair prejudice. (9)
However, other Federal Rules lurk in the background to complicate the inquiry. First, Rule 404's prohibition against using character evidence to prove conduct seeks to limit the jury from drawing the inference that character traits and past conduct predict present behavior. (10) Even an entirely accurate "Convicted Murderer Profile" raises serious concerns that the defendant will not receive a fair trial. The Convicted Murderer Profile invites the jury to conclude that because this defendant fits the profile, he or she is more likely to have committed the crime. Rule 404 seeks to prevent the jury from drawing precisely this "forbidden inference."
Rule 404(a)(1) declares that "[e]vidence of a person's character or character trait is not admissible to prove that on a particular occasion the person acted in accordance with the character or trait." If one defines fitting a profile or possessing a syndrome (11) as "character" or a "character trait," (12) the Rule should operate to exclude the evidence, unless an exception to Rule 404 applies.
When dealing with profile and syndrome evidence, the majority of jurisdictions attempt to mitigate Rule 404 concerns by restricting the admissibility of such evidence as proof of substantive guilt, while generally allowing it for other purposes, such as explaining conduct. (13) That is, courts focus exclusively on the purpose of the evidence, rather than generally prohibiting it because of the forbidden inference it invites. …