(1) A person commits perjury in the first degree if in any official proceeding he knowingly makes a materially false statement, which he does not believe to be true, under an oath required or authorized by law.
(2) Knowledge of the materiality of the statement is not an element of this crime, and the defendant's mistaken belief that his statement was not material is not a defense, although it may be considered by the court in imposing sentence.
(3) Perjury in the first degree is a class 4 felony.