The insanity plea is said to be a difficult one to prove. But cases involving insane criminals over the years reveal that many mentally-ill killers don't attempt to cover up their crimes. They don't run away from the scene, and they don't lie. The truly insane usually own their offenses.
From being dubbed "John Doe Duffle Bag" by authorities, because a duffle bag was the only clue they had early in the investigation into the three murders, to "Son of Sal," Salvatore Perrone murdered three Middle Eastern shopkeepers before police stopped him.
Perrone tried to enter an insanity plea but was deemed fit to stand trial. He wished to defend himself, which is viewed as a tell-tale sign that one is insane, but the judge denied his request. The "Son of Sal" faced his crimes as a sane serial killer like John Wayne Gacy and Jeffrey Dahmer before him. Unlike Gacy, Perrone would not be put to death. He received mercy, and the judge told him so.