The first Victim appears to be opposite the stairs at County building (top left of picture) which means he was in the bike lane/on the pedestrian path at the beginning of the bridge, and not in the middle of the bridge. He took out a Postcard Stand:
First reports... Fog of war.
But, as you point out, the attack started on the river bank opposite. They need to extend their imminent threat/possible diversion zone for better blocking. A car or truck bomb would have been devastating.