In any case in which the defense has offered substantial evidence of a mental disease or defect excluding the mental state required as an element of the offense charged, and the jury returns a verdict of “not guilty,” the jury shall also answer a special question in the following form: “Do you find the defendant not guilty solely because the defendant, at the time of the alleged crime, was suffering from a mental disease or defect which rendered the defendant incapable of possessing the required criminal intent?” The provisions of this section shall be in force and take effect on and after January 1, 1996.