Evidence of a criminal or wrongful act apart from the act that at issue at trial Is not barred by the prohibition against circumstantial use of character if intent, knowledge, mistake, or accident is a legally-material factual issue, the opposing party suggests the non-existence of knowledge or urges mistake or accident as a defense, and evidence of another crime, wrong, or act is offered to prove the knowledge or the absence of mistake or accident by a criminal defendant or other person.

Cf. United States v. Bedonie, 913 F.2d 782, 799-801 (10th Cir. 1990) ( "Fed.R.Evid. 601 provides that '[e]very person is competent to be a witness except as otherwise provided.' 'A witness may not testify to a matter unless evidence is introduced sufficient to support a finding that...A person can be qualified to serve as a witness -- a person can be a competent witness -- even if he or she does not understand or appreciate the duty to tell the truth.

Fed. R. Evid. 415 ("In a civil case in which a claim for damages or other relief is predicated on a party's alleged commission of conduct constituting an offense of sexual assault or child molestation, evidence of that party's commission of another offense or offenses of sexual assault or child molestation is admissible and may be...Federal Rule of Evidence 415 and comparable rules in some states create an exception to the prohibition against "circumstantial" character evidence, the prohibition in Federal Rule against the use of character to show conduct. Rules such as Rule 415 provide that in a civil action which a claim rests on a party's alleged conduct constituting a criminal sexual assault or child molestation, evidence of that party's commission of another offense or offenses of sexual assault or child molestation is relevant and admissible.

Fed. R. Evid. 403 (exclusion under Rule 403 permissible if the probative value of the evidence is "substantially outweighed" by a risk or harm).Relevant and probative evidence may be excluded as "unduly prejudicial" -- to prevent undue prejudice because of emotion, to prevent waste of time, and to prevent other such harms -- only if the risk of such harms substantially outweighs the probative value of the offered evidence.