It's the theory that the driver was the one that assassinated JFK. The moment in question is when the driver turns around after JFK is hit in the throat. People think they see a gun, but it's really the top of the head (hair) of the other SS Agent.
Besides the whole Zapruder film (the version we see today) is in question because it has been manipulated (edited). Watch the interview of CIO Dino Brugioni "zapruder film mystery" who handled the original the day after the assassination. His job was to make copies and make print boards for government officials to analyze later. He remembered more frames in the head shot directly contradicting single 313 frame headshot.
In other words, the Zapruder film has been manipulated because it would have revealed in greater detail what really happened and throw away the lone gunman theory back in 1963.

LOL, I could not even tell that is what this was, all I saw was and audience in the foreground and I was so focused on the circle that the people on the grass hill looked like they were on a stage. Ha !