If you haven’t seen it in your investigations, then I doubt if raw timestamps would help.
First, follow the link in the Youtube description to the FBI page, and download the .mp4 file.
Next, open it in VLC (download it first, if needed), activate “Interactive Zoom” mode (Tools → Effects and Filters → Video Effects → Geometry → Interactive Zoom), set it to 800% (small slider below the left corner of the picture-in-picture) and focus on the edge of the small rooftop building.
Last, look at 0:09-0:10. There is clearly an object of some sort on his back, as his torso is larger in that direction than to his front (relative to his head). It’s more consistent with a backpack than a rifle, but that’s unsurprising given the camera. Annotated image here, but it’s much clearer in video form.
(Those aren’t the parts I was mentioning in the previous comment. That was as he was walking across the grass, which (on rereading) wasn’t your point. This is as he is still on the roof.)
Re #3: The easiest demonstration is to do it. How well do you think it would go over if you said “I know you like cooperative board/card games. I found The Crew for sale at Central Gaming for $19.99, and you might enjoy playing it. Here’s their address and a $20 bill.” vs. just buying it and giving to them?
Kind of against #4: A gift includes permission to have and use it. This goes double when the recipient is a child, spouse, or anyone else the gift-giver has a stake in. “Why do you think those binoculars are the best way to spend $1000?” Not my choice, it was a gift! “Why do you birdwatch during our hikes?” Because I was gifted the binoculars!