The rule seems clear enough: "Evidence 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." Fed. R. Evid. 404(a)(1).
And yet the battle rages on over whether and when the government may present expert profile evidence in a criminal case. The Ninth Circuit weighed in earlier this month in United States v. Wells with a resounding NEVER when its purpose is to prove substantive evidence of guilt.
Wells covers a lot of profiler ground, and is a must-read for any lawyer faced with the admission of this sort of evidence. Bottom line: The use of this evidence to prove guilt violates Rules 404(a)(1) and 403:
"As we have explained, testimony of this nature is "inherently prejudicial," has no place as substantive evidence of guilt, and would therefore fail Rule 403’s balancing test."