I’ve got a new proposition that a professional sniper WAS the gunman at the SE TSBD window, choosing this more difficult scenario of shooting at a moving target, because part of his contract /plan necessitated that Oswald had to be implicated as the suspect.
I see 2 possibilities:
A. this mission to frame Oswald was directed by some higher authority ordering the hit, which compelled the pro sniper to choose TSBD 6th floor.
B. The pro shooter was some rogue CIA pro who had a personal vendetta against JFK and Oswald as well.
In either case, the pro snipers primary mission was to terminate JFK so he chose to use his own precision rifle while preplanting the POS MC rifle in the boxes perhaps a day earlier or in the middle of the night when he was able easily get into the unsecured TSBD.
He fired 3 shots from the SE window, 1st was at Z224, a hit that went thru both JFK and JC. Not the kill shot though. So he aimed and tracked more carefully for the 2nd shot, and hit the kill shot 4.8 seconds later at Z313.
The 3rd shot was unaimed and fired as rapidly(2secs later ) as the gunman could operate his better quality bolt action rifle which he kept the barrel sticking out the window as he did this last shot (which hit curb near James Tague)
The reason to do this was to maximize the rifle barrel being seen stuck out the 6th floor SE window of TSBD to focus attention to that 6th floor window, where 3 MC shells were left the pro shooter (while picking up his own shells and his rifle) with him when he escaped from 6th floor probably using the west elevator.
This scenario preserves the Harold Norman witness having heard 3 shots fired and 3 shells hitting the floor)