Special filtering techniques pierce the darkened areas of the Orville Nix film to reveal a probable second gunman from behind the Pergoda at the upper right. Click on image to enlarge.
This is an oscillating file containing 14 frames that rock back and forth. This demonstrates that the person is following the movement of the Presidential Limousine. Upper right corner. Click on image to enlarge.
The Davis Report 
that position is behind the passing limo.
doesn’t the kill shot come from the near front?