At the time that Altgen's snapped the camera shutter for Altgen #6 Chaney was looking over his right shoulder at President Kennedy as he grabbed at his throat.......
Walt. President Kennedy NEVER, EVER "grabbed" or touched his throat! You haven't been paying attention o the Zapruder film.
President Kennedy's right hand covers his mouth. Left hand is beneath right hand, with the index finger partially curled and sticking up, while the remaining fingers are slightly curled. The extended index finger can be clearly seen in the Altgens photo, too. As the seconds pass, Kennedy turns his head slightly to his left without lowering his right hand, and now his right hand is level with his cheek. As soon as Mrs. Kennedy reaches her husband's left arm and pulls it slightly downward, he then brings his right hand down to his chest where it remained the rest of the way down the street until the fatal shot.
There is zero evidence or proof that President Kennedy's hands went anywhere near his throat, therefore, he never "grabbed' "clutched" or touched his throat. Period.