Yes, but are there not only a limited number who were at the bombed locations around the time of the Marathon. Identifying those - if the evidence about the bombs being in black bags is sound - gives you leads to investigate.
>but saying they may have found the guys responsible is incendiary and dangerous. //
It's also true. They may [huge huge caveat] have found the people.
Personally I think the only real way the public can help is to identify themselves and their family/friends in images that others have handed over or they've sent to the officials investigating (Boston FBI presumably).
I'm assuming that the office based enquiries are based on using available imagery to build a profile of all movements and to list people who may need to be interviewed. I poured over a few images (in one reddit thread) of the area of the bomb outside 671 Marathon Place and it was quite easy to spot certain people hanging around - what surprised me was that there wasn't already more imagery available. There must be many video feeds, CCTV and such in the area, eg from the shops at the bomb sites.