Online hacker Jester posted an interesting pic from Boston day of the race.

[DetlefK]

31. Hard to tell.

First, you compare a black-and-white-photo to a color-photo.
Second, that pattern isn't very unique. By my guess, about 10% of all backpacks have this.
Third, why isn't the neck-handle of the backpack on the right visible in the photos on the left?

But on the other hand:
If you look at the color-photos upper center and right, you can clearly see that he transported something heavy in that backpack, because the shoulder straps are stretched. (The plastic is normally stiff enough to retain some curvature.) That stuff might be sports-goods or whatever though.

Was he walking or was he standing while this photo was taken?
If he was standing, then carrying a heavy backpack like this is okay.
But if he was walking a considerable distance, then carrying a heavy backpack like this is suspicious, because it would bump into his right thigh all the time and turn uncomfortable pretty fast.





Maybe. A BIG Maybe.
And too many open questions. Too much left to the realm of speculation.
But enough to check for finger-prints.