Why do you think they did all this to him?
Seduce him at the start, before show up in the rain, misbehave at his dinner table, blackmail and threaten to accuse him of having underage sex with one of them, knock him out, tie him up, outright sexually assault him if well yes that r word in this case of a non-statutory female on male category, hit him and assault him physically, threaten to kill him, torture him via sound volume increases and headphones etc, and of course bury him and add that YouTube (sorry, Facebook) video insertion and also vandalize his home.
What was their motivation, were they just insane or also driven to it and was he just an inevitably easy target for them, cheers.