What are you seeing in the Nix film you are interpreting as shots?
I believe the reference is to 0:20 in that video. That image is nowhere near the pergola windows. It is halfway down the steps from the pergola. Were anyone there, they would have been easily seen.
It has been studied for years.... and years ago determined to be freaky looking shadows.
If it were a person..they would have to be 3 feet high or less and have a bean shooter not a rifle. Compare with Zapruder and friend who towered over the image.
Perhaps it was a really short aborigines Amazonian with a poison dart but it was not a rifle sniper.
Notice in the video the image does not change shape. Were it a shooter it most certainly would have.
View this video from Mr Nix himself. At 2:20 he tells were he believed the shots came from.....