I don’t think any shot paralyzed him, since he moved his hands, arms, and torso after the first shot hit him. Also, I don’t think the autopsy showed any spinal cord damage, did it?
The movement of Kennedy’s arms was into the ‘Thorburn Position’, a medical term for the movement of the arms along with a high extension of the elbows as a neurological reaction to trauma to the spinal cord.
It’s a fairly common symptom in combat injuries that involve temporary or permanent paralyzation of the high spinal cord region. It’s the most visible indicator to combat medics and Hospital Corpsmen that the subject is paralyzed.