[longfellowsmuse]

I agree with this.

From the new photos that show what appears to be a large bag (the device) sitting on the curb I have a hard time understanding how such a large bag could be just laying there unnoticed. I also find it difficult to understand how it being placed in such an obvious place would go unnoticed...Unless it was placed there by someone who would be deemed trustworthy or someone who is part of the scene and blends in well.

You would think a man dressed in black with his head covered placing a large package right by the road would not go unnoticed, but I have also observed how poor humans can be at situational awareness in crowded conditions where they are extremely distracted ( looking for loved ones finishing a race)

I really hope I’m wrong but I have a hunch it was placed there by someone who would appear to fit in... your volunteer hypothesis fits.

[freeandfreezing]

From the new photos that show what appears to be a large bag (the device) sitting on the curb

But the later image after the explosion shows the railing bent around the mail box in a way that is inconsistent with the explosive charge being in front of the railing where the bag is.

[wideminded]

I have a hard time understanding how such a large bag could be just laying there unnoticed. ... but I have also observed how poor humans can be at situational awareness in crowded conditions

Let us pause to appreciate Richard Jewell, who saved lives by noticing a bag in the Atlanta bombing and then was wrongly hounded as the #1 suspect.

[jonrick46]

I thought both devices were set off in trash cans.