They do it again. Hence this local Washington, DC story. It seems that last night, one Vitaly Davydov beat to death his roommate in a mental facility. As the story notes:
You may also recognize Davydov's name. He was convicted of beating his psychiatrist, Doctor Wayne Fenton, to death in Rockville five years ago.
Now if he was "convicted," what that means is that he was not insane; you can't convict insane people, because a murder conviction requires criminal mens rea and the capacity to understand what you were doing.
I also thought the final paragraph of the story was noteworthy:
Davydov is now charged with first and second degree murder. Police are still trying to establish a motive.
Let me see if I can suggest a motive: He's big and strong and 24 years old, likes killing, and has figured out that society isn't all that serious about doing anything to stop him.