I went to Dallas in '64 with my high school band. Got a good look at how close in the area really is.
From the other corner window anybody good with a handgun could have shot the President at that range with pistol as they stopped to make the turn. And, of course the limo at that window was coming right at you... plus it had to make a dead stop right under the window.
Anyhow, to get a patsy, I think the kill shot was taken from a second story window in the adjacent building by a true sharpshooter.
Makes sense the shot could not be a matter of speculation.