That’s a famous picture from an AP photographer. Altgens, maybe? It’s the only one or two of its kind as far as I know, out of a lot of pics that day. It was included in the “Torch is Passed” book that everybody had in those days.
A Texas congressman travelling with the motorcade that day, Yarborough I think, mentioned that he could smell the odor of gunpowder from the time the shots were fired constantly and “all the way to Parkland”. This is very significant I think, because had shots only been fired from the 6th floor of a building (or just about anywhere else) there’s no way that could happen.
But a negligent firearm discharge from the motorcade itself, yeah I could see that happening. And it does explain a lot of other decisions that were made that day, and following days, and for years after.
That photo os from the 6th floor window. SS is a little late here pulling out their M-14 rifle after they passed under the triple overpass.