I know the Auzzy lot can be hard arses when it comes to the law. But I am sure if you, your gf and her friend and bro all deny knowledge of it happening and just say all her bro knows is at one point his medical card kept going missing things will be fine. That is if the subject even comes up. Which I highly doubt because Mr Psycho would be incriminating himself in the process. Plus it will get him deported and all that lovely jazz. A lot worse than what will happen to her or her brother. Use this argument to win her over. Also tell her if she doesn't do anything soon she'll end up a lot worse than she is now. Because his behavior is not that of a normal sane person. It is boarder-lining that of a psychopath. And the next step will be her ending up in hospital. He has already harmed her once. What is stopping him doing it again and doing worse while he is at it?
Also from how this guy sounds I don't think direct confrontation will get anyone anywhere. So no asking to leave. He'll most likely flip a lid and it will definitely make things a hell of a lot worse. He knows he has her under his control. The moment she shows other wise he will not be happy, and most likely lash out.
As far as I know... no matter what your criminal past is (unless you did something massive.) the police have to treat all victims equally. Right now she is the victim of a serious crime. So unless she has served prison sentence for something major just go to the cops, or like Jakk says go to private lawyer and get advice on what to do next.
*Edit*
Here is some information on Stalking:
http://homepage.psy.utexas.edu/homep...kingWhyAm.html
http://law.jrank.org/pages/10451/Stalking.html