(a) Reputation or Opinion. In all cases in which evidence of a person’s character or character trait is admissible, proof may be made by testimony as to reputation or by testimony in the form of an opinion. In a criminal case, to be qualified to testify at the guilt stage of trial concerning the character or character trait of an accused, a witness must have been familiar with the reputation, or with the underlying facts or information upon which the opinion is based, prior to the day of the offense. In all cases where testimony is admitted under this rule, on cross-examination inquiry is allowable into relevant specific instances of conduct.
(b) Specific Instances of Conduct. In cases in which a person’s character or character trait is an essential element of a charge, claim or defense, proof may also be made of specific instances of that person’s conduct.