I have seen this image doing the rounds of Twitter, and now also on Facebook (see below).
I may be wrong - please correct me if I am - but it seems to imply that we can identify the Boston bomb culprit by the lighter-coloured fabric strap on his backpack.
This is our investigation process??
Perhaps it is him, I wouldn't know. But just to assist with the elimination process: I also have a backpack with those grey strips on the arm straps. In my case at least it is a Victorinox backpack, extremely popular piece of luggage I see on people at least several times a day. But it wasn't me.