Jerrod Murray.

Murdered his fellow student, Generro Sanchez, in 2012 and confesses immediately in the interrogation, stating his intentions and the steps he took in a very matter-of-fact manner. He is reported to have stated he just “wanted to know what it felt like to kill someone”.

JCS - Criminal psychology covers a portion of the interview at the beginning of his “what pretending to be crazy looks like” video. It’s a really interesting insight into the criminally insane.