To anyone still following my amazing misadventures,
I woke up this morning to find house-mate #4 laying down the law. Turns out no one opens the door in the morning, it's all the one guy and now I know at least two of us have had it. For now the problem has gone, but at the cost of fuelling his paranoia that we are all out to get him as a group. One more thing and I'm getting him kicked out.
Thanks for all the advice guys, it's cool to see how the crowd thinks.