This is what I mean about circumstantial evidence:
So the FBI told us that Jahar and Tamerlan deliberately went to the marathon to bomb it.(no proof) Jahar and Tamerlan stop to discuss their plan, split up to place a bomb at each spot(no proof). They wait, and Tamerlan drops the bag and continues walking then, Jahar essentially called the device to detonate it(no proof).
Under different circumstances:
Jahar and Tamerlan were on their way to a destination, they knew it was marathon Monday and decided to walk through Boylston st. Jahar and Tamerlan both stop to see the people run by, Jahar isn’t paying attention and Tamerlan walks ahead of him. He stops, looks around and can’t find Tamerlan. He picks up his phone to call tamerlan to see where he went, but puts his bag down while he looks around to find him(its super crowded) as he calls, the bomb detonates and hes in shock by it so not even thinking of grabbing his bag he runs.
See how its nothing that has proof, hardening evidence that they did it? Even the video, as described in the indictment, shows jahar “apparently” slips his bag onto the ground, which means they are guessing, they don’t even know themselves. If the media weren’t constantly feeding this to people, they wouldn’t believe it so much.