Presumption of culpable mental state requires accused prove lack of mens rea; mens rea must be shown beyond reasonable doubt. Where an offence under the Act requires a culpable mental state, the court shall presume its existence in prosecution, but the accused may defend by proving absence of that mental state concerning the charged act; the statute defines culpable mental state to include intention, motive, knowledge, and belief or reason to believe, and states that a fact is proved only when believed to exist beyond reasonable doubt.