Donald Salt is an ex-con who appeared on Castle episode "Tick, Tick, Tick…". In the pocket of the corpse of Michelle Lewis inden investigators the impression of his little finger, which was also found at the Grand Central Station. In front of the building where he lives, he is stopped by Castle with a stun gun. However missing Salts little finger. Under interrogation, he said that someone offered him $ 5,000 on the Internet for this.