Looks like he was the bomb maker -- my guess is when he couldn't get in the stadium, his handlers blew him up before he could transfer everything to the vest. Two-way radios would make sense.
hmmmm...
then, at least, he was the exception to the rule at least with the building of the bomb...
I wonder if he was on any drugs at the time? Generally the bombers are doped up pretty well....
It occurred to me that the explosive could have been on a timer rather than remote detonated, but if he had made the bombs he wouldn't have been dawdling unless his imminent "martyrdom" distracted him.