Rule 609.1 Evidence of bias, interest, or motive. (a) General rule. The credibility of a witness may be attacked by evidence of bias, interest, or motive.

(b) Extrinsic evidence of bias, interest, or motive. Extrinsic evidence of a witness' bias, interest, or motive is not admissible unless, on cross-examination, the matter is brought to the attention of the witness and the witness is afforded an opportunity to explain or deny the matter. [L 1980, c 164, pt of §1]