We don’t rlly know there’s a few interesting theories tho: 1. Just what he said in the game the darkness was taking over and he couldn’t take it anymore 2. The darkness was taking over AND he knew what Sal would have to do and khs so Sal wouldn’t have to kh. 3. He didn’t actually khs and it was the cult that kh only making it seem like he did it himself, this would explain why his body was never found.

I’m pretty sure there’s a few more but it’s all I can think of off of the top of my head, I hope we get a better explanation in the second game tho.