Darn it, had a brain fart here but isn't there a thing where if there are ANY issues involving a property... taxes, old murders, EASEMENTS... that you have to come clean about them totally BEFORE selling or else you're in big trouble?
If this guy has gone and gotten a paper traceable lean basically on this property then it should have been mentioned when they were looking at the house.
AH... DISCLOSURE... that's it. Does Cali have laws about disclosure? I've heard of cases where something wasn't talked about and then found after the fact and the seller and/or realtor who lied (and yes, omitting info in a disclosure state is lying) were responsible... some have to buy back the house, some just have to pay fines, etc.
I'd definitely look up the laws there and see what can be done.
Also, just because one owner didn't fight this guy (maybe they tried and that's why the jerk went to court to get this right to trespass and there was nothing the owner could do about it?) doesn't mean that YOU have. The property has changed hands... what if you wanted to put a fence up? Would you have to ask this jerk for permission to do something on your own property... totally bogus. Fight Fight Fight! This guy is a cheat... wants to steal other people's property rather than buying more for himself.
edit... n'mind see your friend already dealt with the jerk!