Certainly true that somebody stacked the book boxes so as to provide a gun rest so I'll assume the shooter used them in the shooting. That has nothing to do with how the shooter was situated while the limo was on Houston.
Also assume that this was an accomplished** shooter....who was obviously positioned with help.
About the clip @ 1:48 --there is a difference between 'developing' the film and printing the pictures which Dillard said he did.
Perhaps he doesn't remember who developed the film as there was always a tech on station to run films that are brought in from news people.
However...Really, nobody takes a picture with one camera and in the moment of newsworthy photography--switches cameras.
Of course, I don't know what kind/model camera was used. Ball should have inquired but then I don't think he really cared.
**By accomplished shooter I certainly don't mean Oswald-- who acquired a marksman rating some 3-4 years earlier which every marine in the corps is required to do. And just because of that-- the derelict mind who knows nothing about shooting equates this one average feat as having produced an expert sniper for the rest of his life. ODIABS
Perhaps shots were fired from a window on the opposite side of the floor [pigeons flew off the roof]