substitute
(7) If the trier of fact is satisfied that a person is not criminally responsible for an offence only because of mental impairment, it must—
(a) for an offence dealt with before the Supreme Court—return or enter a special verdict that the person is not guilty of the offence because of mental impairment; or
(b) for any other offence—find the person not guilty of the offence because of mental impairment.