A fact check, as a counterpoint:
https://www.google.com/amp/s/mobile.reuters.com/article/amp/idUSKBN277200
From the research I have done, it also appears to be standard for some Marines to face the Presidential motorcade and for some to turn their backs (for security purposes). You can see a comparison online of the Biden vs. Trump inaugurations, and the military officers were in the same formation (some with backs turned) for Trump.
Re: your question, it looks like Biden did in fact receive a 21-gun salute...
Genuinely curious, is the theory that there was no actual bombing or manhunt at all? Or that the bombing was staged?
I ask because I was living right outside Boston at the time. I didn’t attend the marathon, but friends and family were present. None of them were injured, but they certainly witnessed a large explosion and total panic.
We were living on the border of Watertown, where the perps were caught. Maybe 1-2 miles down the road? Again, I was not a direct witness but was close enough to hear the sounds of a firefight and improvised explosions between the police and the suspects. This all took place in a residential neighborhood with lots of people watching from inside their homes. As far as I know, there was no evacuation of potential witnesses - everyone was told to “shelter in place.”. So there was certainly a commitment to a very realistic “show” if nothing else. How do you understand what was really going on there?