I'm really at a loss with this one. Clearly something happened on the way back to his friend's house. Robbery seems like the most likely motive, but why he would be killed over it and undressed is an excellent question.

It briefly crossed my mind that maybe his friend was involved somehow, but he likely wouldn't be a criminal mastermind and you'd think the police would have caught on to that.

I suppose it's always possible he was involved in something he shouldn't have been, but I would think his girlfriend or a friend would have mentioned something by now. I would really like to see this case solved.