CNN just reported that the police have ruled homicide and that he'd been shot in the back of the head. Which says to me that either someone got the drop on him or he was executed. They also said there were firearms "in the vicinity" but they didn't say if they were easily accessible. If they were easy to access, then I'm guessing he probably knew his attacker.
Yay for armchair criminology!
Not necessarily that he knew his attacker. Also, it depends on which guns. His? Was one of his weapons used? If it was, and he was killed by it then he may not have known his attacker at all. But the attacker knew him and where his weapons are.
But meh.