The pock mark you see on the ground is almost certainly the bomb location.. Any residual smoke cluster you see is a result of areas affected by the outburst of the bomb. Smoke would appear around the perimeter of the bomb, not just at the bomb's location.
I do see something which might be on the ground behind the guy on the right in the 'before blast' photo of the two guys. What's odd about guy on left is his shirt has white logo on front which does not appear in any other photos of him.
This is another 'after blast' photo.. Something to think about.. The 'white hat' brigade:
hmmm drudge reported yesterday that Lord and Taylor video showed white hat backwards with grey hoodie... this certainly fits the description.
Fox is reporting clear image shows a person who is “young” and “white” ....occupy crowd?