My guess is that SOP for major crimes is for the cops/feds to go to surrounding homes and businesses to ask for any security footage they might have.
There’s a good representation of this in “Patriots Day (2016)” about the Boston Marathon bombing. Which is a pretty good movie for those who haven’t seen it,
Ok, so what I did was get a streetview that matched the picture above in this article. Then I rotated the view exactly 180 degrees to see where the camera view is coming from. You will see it is coming from the direction of the Fairchild building which is beyond the corner of the fence and the parking lot on the other side of it.
However, now that I’ve looked at it, I suspect that a better guess is a camera that is on the post just above the red light... This is on a post that also has the street name shown...Washington Ave SW.
https://www.google.ca/maps/@38.8839007,-77.0091129,3a,75y,33.94h,94.44t/data=!3m6!1e1!3m4!1sf38eymgeJB5Z_jAVOjPwLg!2e0!7i16384!8i8192?entry=ttu
Basically, what I was wondering is “who could have supplied this footage?”