Honestly, first off,
MA support will do ABSOLUTELY NOTHING!! I am afraid you will have to get used to this. In 9 out of 10 cases you will get an answer like "read the EULA we are not responsible" or something along those lines. Honestly, the more you deposit the better the service you seem to get from support. I know of a couple of cases where
MA has monetarily compensated people for trouble (I have had it happen) and things like that. It just seems to happen with the bigger depositers.
As for what I think should be done, I think BOTH players should be banned. Someone stealing from you does not give you the right to steal from them so why should it be any different here? I think when the newbie decided to start the whole standing between thing, he became just as guilty as the person who started kill stealing from him.
In my opinion the best answer here is call some big dmg/sec soc mates and create a team and team hunt for about 15-20 minutes. I think you will find this makes the KS'r go away quickly and is within your EULA given rights.