Presumption of culpable mental state shifts evidentiary posture but allows accused to rebut absence of mens rea. Where an offence under the Act requires a culpable mental state, the court shall presume its existence but the accused may defend by proving absence of that state regarding the charged act; 'culpable mental state' includes intention, motive, knowledge, and belief or reason to believe a fact, and a fact is proved only when the court believes it beyond reasonable doubt rather than by a mere preponderance of probability.