Upon a finding of incompetency to stand trial under section 403¹ after an acquittal by reason of lack of responsibility under section 404,² or following an examination in aid of sentencing under section 405³ the attorney for the Commonwealth, on his own or acting at the direction of the court, the defendant, his counsel, the county administrator, or any other interested party may petition the same court for an order directing involuntary treatment under section 304.⁴