(a) In a prosecution for a crime when the affirmative defense of insanity is raised under AS 12.47.010, or when evidence of a mental disease or defect of the defendant is otherwise admissible at trial under AS 12.47.020, the trier of fact shall find, and the verdict shall state, whether the defendant is
(1) guilty;
(2) not guilty;
(3) not guilty by reason of insanity; or
(4) guilty but mentally ill.
(b) To return a verdict under (a)(4) of this section, the fact finder must find beyond a reasonable doubt that the defendant committed the crime and that, when the defendant committed the crime, the defendant was guilty but mentally ill as defined in AS 12.47.030.
(c) When the jury is instructed as to the verdicts under (a) of this section, it shall also be instructed on the dispositions available under AS 12.47.050 and 12.47.090.