The person [...]wearing black jacket, tan slacks and boots, is part of a larger group all dressed the same.
In the wider view, it is clear this is after the bombing. But they are not helping the victims, nor searching for clues. Although dressed in uniform, they show no insignia at all, not even for police or fire department. And they seem to be wearing the same backpacks used to conceal the bombs.
[...] Here is another picture of the men in black and tan (lower left) leaving the scene.
These men are not first responders or they would be helping the victims. They are not law enforcement, or they would be helping with crowd control. They are not bomb disposal squad or they would be looking for more bombs.
So who the hell are they?