LPT Request: how do I prevent an eventual theft from my cousin?

My cousin has been coming into our home half drunk taking stuff from the fridge and also other stuff laying around. My mom doesn't do anything about it because he's "family" and even if we locked the door my mom would let him in. He would bang on the door in the morning drunk screaming according to my brother. What I'm worried is that he might eventually steal things. He's a habitual drug user and has a history of stealing things and getting into fights.

he doesn't live here, he only moved to my country recently for work (but got fired cause he got into a fight) so he's on a work permit. I don't want to come home eventually with my stuff stolen. How do I solve this without getting myself into trouble? I'm not worried about burning bridges.

EDIT: I'm trying not to do anything rash on account of my mom. She may not be on my side in this situation but her mental health comes first. Ratting him out is no problem, but I wouldn't want her to take the hit from toxic relatives who's enabling his behaviour.