In November 1990, Shawcross was tried by Monroe County First Assistant District Attorney Charles J. Siragusa for the 10 murders in Monroe County. Shawcross pleaded not guilty by reason of insanity, with testimony from forensic psychiatrist Dorothy Lewis that he had brain damage, multiple personality disorder (now known as dissociative identity disorder) and post-traumatic stress disorder, and had been sexually abused as a child. Lewis also claimed that Shawcross moved into a separate internal personality named "Bessie" when he killed, arguing for Shawcross to be institutionalized rather than being returned to the prisons system.