There isn't any telling what kind of horrors he suffered before you got him.. May I suggets this..

When you see he has done it, scold him then shut him up in a bathroom or some other small room for about 30 minutes. Do it EVERY time and be consistant. Ignore his crying to get out.. This is a "time" out for him.. Of coarse, have food, water and litter box in there.

I tried this with Samantha when she wouldn't stop attacking my other babies and there was a territorial struggle going on with them.. It only too her THREE days of this to learn and there has been no attacks from her since. They HATE being in a room with the door shut and being alone.