I'm uncomfortable with police shooting people, but if a bomb has a triggering mechanism and detonator attached, it really only takes a second to press a button and trigger it. Something like this:
http://www.swatheadsets.com/PTT/ptt2.html
(Specifically, PTT RP7)
...would be pretty easy to make yourself. I don't know how you stop somebody with a trigger like that from pressing the button.

I'm withholding judgement until I hear more details. If the police knew that he had a bomb belt on, and he refused to stop, it starts to sound like their actions may have been justified. If he simply didn't stop, then clearly this was a ridiculous over-reaction.