From the Defeated: Part 1 - S6.E5

Two young men are found murdered, the only connection being that skin from one of them is found under the other's fingernails. As other bodies are found, Tony deduces that a sadistic gay murderer is abducting white boys and forcing them to kill each other. Meanwhile Michael Bryant, the cannibal killer whom Tony helped to put away, sends him a message from the secure unit where he is incarcerated, telling Tony that he is planning to escape and will see him soon.