President Kennedy - the unseen turn onto Elm

Someone destroyed every film taken of Kennedy's limo turn onto Elm St. But this one may tell why. It's of Kennedy receiving the first shot, which possibly may have singed him. Why else does the Zapruder film have footage of the motorcycle cops but is spliced when Kennedy makes the turn onto Elm St.?. Someone said Zapruder turned off his camera and then turned it back on when Kennedy was already on Elm. Watch the way he pulls back his hand and how his fingers fold unnaturally..