Homicidal ideation does not always equate to wanting to live with having killed someone, and a lot of these people are closer to normal than they realize until they are facing potential consequences for their actions. I would posit that killing oneself after doing something so heinous is one of the saner outcomes.

A lot of people experience “fucked around, found out” immediately or shortly after they cross a line, before anyone else has a chance to tell them they fucked up.