What caused Jeffree to fall over the fence and not wake up

In the section where Jeffrey is found by Grayson? If so, we aren't specifically told. Possibly he fell because it was dark.... because he lost his footing. Please provide a chapter number, as I cannot be sure without specific information.

Only, one morning the stranger falls from the fence and lies on the ground, on the other side. It doesn't move. You try to poke your nose through the chain links, but you can't reach, you can only watch ... only watch.