This is mere seconds after the explosion took place, with the smoke still drifting through the air. Already they've made it to the side of the most obvious casualty; I can't really see the basis for your comment.
Yes. At least four of them are running away from the bomb site, the other two are staring at a fallen athlete. Maybe they though he was shot or something, I just can't make sense of it, hence the question.
After 9/11 (and umpteen IED in Iraq and Afghanistan), it was drilled into most emergency services personnel NOT to rush on the site of an explosion, for fear of secondary devices.
These guys are doing that: moving people away from the blast area, both for their safety and to make it easier for paramedics and bomb squad to reach it, while helping whoever cannot move.
I usually don't like police forces the world over (and Boston has some nasty precedents), but this picture makes them look well-trained, reactive and downright heroic -- which is probably not the case, they're just professionals trying to do their job.
Generally speaking, the one place a criminal is not is the scene of the crime. Explosion over there? If the criminal is still around, they are not going to be at that site (and if they are, they're not in a state to worry about further criminal action coming from them).
