A story like this is frustrating because we just don’t know, and cannot know all the facts. So we just project our own issues onto it.
What we do know though, is that the guys admits murdering them and moving the bodies, the girl while still alive, before he finished her off with one under her chin.
We also know that after moving the bodies, he waited until the next day to do anything about it.
Post 55 mentions some details.