Looking further at the video, I matched it up with Google streetview.
The two suspects coming south on Gloucester turned left onto Boylston where they walked east, in the same direction as the runners, and were captured on the time stamp of the video at about 2:38 p.m. That's a block and a half from the second blast site and two blocks and a half from the first blast site. So clearly the video was not reversed.
Since the bombs detonated at 2:47 p.m. those two did NOT dawdle anywhere. They walked straight to their target spots, deposited their bags and then at least Suspect #2 the white-hat guy returned the way he came but turned north one block short (on Fairfield) of the way they came, as it appears from the high-res photo.
That’s some squared away investigative work. Thanks, I haven’t even looked at street view yet.
I’m hoping more photos will come out to answer some of our questions.
Suspect # 2 is following about 30 feet behind, Bridgestone cap, tan pants are obvious, both exiting or about to exit to the north on Fairfield, which is the direction they came from. (Cambridge a few blocks to the north across the bridge crossing the Charles River).