I think he still has his thumb partially underneath the backpack strap on the second photo. The backpack is hanging pretty low on his back and I think it is being blocked by his body.
Thats what Iam thinking to his thumb is under the strap in the 2nd picture.
I don't see why anyone expects to see the bomber after the bomb--
My theory--the bombs were in the trash can the night before. Why did so many people get their legs full of shrapnel? That suggests to me that the explosion happened close to the ground, where legs and small children are. People have been at the corner all day, throwing trash on top of the bomb. Accumulation of trash and position of the bomb suggest to me that it was there from the start of the day.
I'd like to know when those cans were placed, when they were last cleaned. Were they brought in special for the run? Can bomb-sniffing dogs smell one of these bombs made in a pressure cooker? (I guess the pressure cooker, which has a strong seal...you know, I don't know why a pressure cooker makes a bomb more than another pot would...)
How many devices in total did they find?