Ok, so if you were a bank robber, wouldn't you want to make sure that the guy actually got back to you with the money? So why would you have the bomb actually go off?? And if you're smart enough to build a bomb, wouldn't you put a tracking device on it so that even when the time ran out and the guy figured he could get away, that you could track him down? And why, if someone else put the collar on him, didn't he just run straight to the police? Was the killer close by??
Personally I think it was murder... but it's so hard to tell.