This is from Moorman... Looks like a gunman or a spotter...

A subsonic 6.5mm or 5.56 mm round fired in a short barrel 10” rifle with suppressor and no one would have heard it.
But this position from the GK pergola would be shooting laterally at a moving target so I’m not sure a professional would choose this spot on the GK where Betzner and Willis are pointing cameras at and where lots of the crowd are looking at.
There is no indication on the JFK lateral skull X-rays that there was damage on the left side of the skull where such a lateral shot from the GK pergola would have exited , except possibly the Harper fragment if it came from the top of the skull ( which is debated).
Nonetheless, the mystery man in black walking away along the low wall from this GK pergola location seconds after the head shot at Z313 is an amazing coincidence to consider.