(1) In any prosecution for an offence under this Act which requires a culpable mental state on the part of the accused, the court shall presume the existence of such mental state but it shall be a defence for the accused to prove the fact that he had no such mental state with respect to the act charged as an offence in that prosecution. Explanation.- In this section," culpable mental state" includes intention, motive, knowledge of a fact and belief in, or reason to believe, a fact.