Zap filmed from an elevated position in the sunshine, not under a dark canopy of trees. Moreover, Zap and Sitzman appear in several films and still photos taken that day; Arnold doesn't.
Lotta stuff happened that day that have never been corroborated by witnesses or images. Such as SA Lem Johns jumping out of the LBJ SS Car and then running down Elm St, or Motor Officer Hargis running up to that little brick wall, or Sitzman immediately running down the knoll and being confronted by a G Man, or the Black Couple sitting on the bench and then running up The Steps as the JFK Limo went under the Triple Underpass, or Emmit Hudson being on The Steps period. (Hudson is the only person to ID Hudson). Personally, I believe there is a corridor from the N-S Picket Fence to roughly the Stemmons Sign in which many things happened that have simply been erased. Gordon Arnold said in his Sixth Floor Interview that 25 yrs later he could not remember with certainty exactly where he was standing while filming the JFK Limo. I believe Arnold was probably standing on a dirt hill/mound closer to that big tree that is about 3 ft out from the picket fence and back toward the shelter behind Zapruder. Roughly, Arnold was a tad (S) and (E) of that tree/ between that tree and the cement walkway that led to The Steps.
