<human>: So im moving in with my step sister in a few weeks to go to university and for the last year she had another housemate who's ex girlfriend has a restraining order on him because of physical abuse, my step sister felt uncomfortable living with him. He was given three months notice that he had to go as was required by the contract he signed and moved out a few days ago and i hoped i'd never hear of him or see him again.

Last night he blew up my step sisters letterbox and even sent her a txt message saying he did it, she went to the police and they apparently told her they cant do anything.

Im sorta worried that he'll do something again but have no idea what to do if he does... call the police is obvious but what if he breaks in? could reddit maybe give me some advice?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: crazy guy blew up house Im moving into's letterbox, might get worse, what can i do if it does?