Dude, don't do shit i know loads of people who act in the same way only when they are drunk , my hometown was destroyed in the war 16 yeras ago, and most of the people i know where in the same situation as your friend, and yes they go krazy every weekend when they get drunk , they threaten to kill somebody or some shit like that but they don't do nothing , my advice is keep away from him and that's it, the worst thing you could do is report him to the authorities , trust me.