But that's not what he said. He said "at the time that he was firing the gun".
Mr. BELIN. At the time you saw this man on the sixth floor, how much of the man could you see?
Mr. BRENNAN. Well, I could see at one time he came to the window and he sat sideways on the window sill. That was previous to President Kennedy getting there. And I could see practically his whole body, from his hips up. But at the time that he was firing the gun, a possibility from his belt up.
Brennan is talking about the two incidents when he saw the gunman. Not that he saw the gunman "from his belt up"
all during the shooting viewing.
His affidavit lays out the timeline:
"I was looking at the man in this windows at the time of the last explosion.
Then this man let the gun down to his side and stepped down out of sight.
He did not seem to be in any hurry. I could see this man from about his belt up."
His testimony:
"He drew the gun back from the window as though he was drawing it back to his side and maybe paused for another second as though to assure himself that he hit his mark, and then he disappeared."
Seeing the gunman "from the belt up" was at the very end, just before the gunman disappeared from view. I think the gunman must have stood up in order for Brennan to see the rifle being drawn to his side.