Right. Of course, on hearing that second gunshot they would have completely forgotten about hearing the first "horrible, ear-shattering noise" (as Mary Woodward described it) 4 seconds earlier and have no sense of the relative spacing on hearing the third 2.3 seconds later. The 40+ people who recalled that same general shot pattern 1.........2.....3 in many different ways, were either all hallucinating together in the same way or actually heard such a pattern of shots.
I can see you're a defense attorney.
So when Hickey said he saw it and remained focused on the President from before the second shot to after the third, he was making it up.
It is odd, then, that we see this after Hickey has turned forward after z255
We don't know for sure if Hickey did turn around right after Z255 but he presumably witnessed the head shot.
(he is still looking rearward at z255 in Altgens 6):
Click to see a close up of frames z272-z277:
I guess it is just a coincidence that we see what Hickey described seeing at the time he says he saw it when he could not really see it at all.
"After a very short distance I heard a loud report which sounded like a firecracker.
It appeared to come from the right and rear and seemed to me to be at ground level.
I stood up and looked to my right and rear in an attempt to identify it. Nothing caught
my attention except people shouting and cheering. A disturbance in 679X caused
me to look forward toward the President's car. Perhaps 2 or 3 seconds elapsed from
the time I looked to the rear and then looked at the President. He was slumped
forward and to his left, and was straightening up to an almost erect sitting position
as I turned and looked. At the moment he was almost sitting erect I heard two reports
which I thought were shots and that appeared to me completely different in sound
than the first report and were in such rapid succession that there seemed to be
practically no time element between them. It looked to me as if the President was
struck in the right upper rear of his head. The first shot of the second two seemed as
if it missed because the hair on the right side of his head flew forward and there didn't
seem to be any impact against his head. The last shot seemed to hit his head and
cause a noise at the point of impact which made him fall forward and to his left again.
-- Possibly four or five seconds elapsed from the time of the first report and the last."
It seems Hickey would have been turned around during the second shot, if he's taking half or the "four or five seconds" he estimates for the shot span to be turned back. About midway through the shooting, he recalls turning back and seeing the President slumped but beginning to straighten up, although the Zapruder film shows the President never straightens up ("almost erect sitting position").
I don't know why Hickey claimed he was facing forward for the last two shots; maybe it wouldn't look so good on paper that he's looking backward as the second shot is heard. But it could be he had yet to look back when he saw a shot strike the President in the Z220s that made the President slump, maybe causing his hair to finch. If that's the case, then putting on paper that he witnessed the President slump (Z220s), then looked back (Altgens) wouldn't look good, either.
The only other thing I can think of is that he heard the fatal gun shot and the impact on the head as separate sounds. Thus he heard the impact on the President's head first and saw "the hair on the right side of his head flew forward". A split-second later, Hickey heard the report from the rifle. He does mention "a noise at the point of impact" but it's out of sequence for my scenario.
There are a few things in Hickey's report the Zapruder film doesn't bear out. Could be he recalled things as best he could, with minor details getting transposed inadvertently. I am fairly certain Hickey couldn't see to the hair flutter in the Z270s.