No, the question that begs to be answered is why do you think it was LHO?
PS. Brennan did not claim to see a rifle being fired. At least, not in his WC testimony.
Who else but LHO? Funny place to store his rifle.
Brennan's first statement to the press was he saw him fire a second time.
Dallas Morning News SaPersonay Nov 23, 1964 ---- The Assassin Crouched And Took Deadly Aim by Kent Biffle
"After the first shot, I looked up and saw him. The gun was sticking out of the window. I saw him fire a second time. He was a slender guy, a nice looking guy. He didn’t seem to be in no hurry.” said Brennan.
FBI Report 11/22
“…... He said the rifle was pointed in the direction of the President’s car when he saw it fired.”