This looks like the second bomb, the first (based on overhead pics yesterday) was on a much wider area of sidewalk and left a scorch mark near the building.
Pinging an expert.
I agree .. because the barrier is different than at the first site. The first site barrier was higher and thicker than the one in the picture.
I’m seeing same color and outline in the fogged area of the second pic.... IMO that suspect package was still there post blast from what I can see.... Same colors, same distance from the mailbox.
Don’t think it was the package from what’s available .... As Sarge K stated, the barriers are wrapped around the mailbox indicating the blast was behind that front row of victims.... I’m guessing the base of the tree behind them.
In my profession all the experts are dead ....:o)
Stay safe !