Not even 12 hours has passed so it's a tad early to judge if he's innocent or not
What I've read and heard from eyewitnesses on TV, I'm on the cops side.
The guy didn't stop when told so.
He was running around in a big, bulky overcoat that didn't fit the current weather situation. Remember that everybody is looking for foreigners with backpacks, much better to strap the bombs to your body and cover it up with an overcoat, right?
When he fell/was tripped by the cops (I've heard both stories), he was shot with 5 rounds. He most likely has the detonator in the hand, pocket or up the arm. If they stop and ask him what he's doing, he can easily reach the detonator. Shoot to kill.
The cops are instructed to shoot to kill. The guy had done enough to justify the cops action.