I reckon that Hoffman's Falcon passed Officer Murphy as Murphy spun to dash across the overpass.
Its like this. A close look at the frames shows that the Falcon was going at 3.3 yd/sec for almost all of its 59 yd & 19.0 sec traject, ie from when/where the Falcon appears
until when/where it stops next to the gawker sitting on the western barrier.
The Falcon has to travel 38 yd to get to the conflict point where Murphy crosses, which takes the Falcon 11.5 sec at 3.3 yd/sec.
Meanwhile JFK has to cross the triple underpass which is 40 yd wide, & then go 147 yd to reach Murphy, totaling 187 yd, which at say 35 mph or 17.2 yd/sec takes 10.9 sec.
And we can add say 1 sec for Murphy to have a half look at Queen Mary approaching him, which makes it 11.9 sec.
So, when Murphy spins round he sees that the Falcon is already passing, & there is no conflict with the Falcon.
Murphy dashes across 24 yd to the western side on an angle to catch a late glimpse of JFK.
The Falcon continues another 21 yd & 7.5 sec before stopping well short of the end of the stationary queue of cars, koz Mr Passenger is yelling to stop.
Mr Passenger jumps out 1 car length before the Falcon has stopped rolling, & he looks north west to see the rear of the JFK limo well up north along the on-ramp.
After passing under Murphy the JFK limo takes 3.5 sec to reach Hoffman's Lookout, which is made up of 25 yd to cross the overpass plus 45 yd to get to the Lookout totaling 70 yd at 41 mph or 20.0 yd/sec.
3.5 sec plus 10.9 sec totals 14.4 sec for the limo to get to Hoffman's Lookout (after we first see Hoffman's Falcon)(ie after the JFK limo is seen entering the triple underpass).
The limo takes another 4.0 sec to go the additional 105 yd to the rail bridge, ie a total of 18.4 sec.
Whilst the Falcon takes 19.0 sec to stop near the gawker sitting on the barrier.
Mr Passenger jumped out over 1 second before the Falcon stopped, ie at 18.0 sec, & Hoffman jumped out say 1 sec after it stopped, ie at 20.0 sec.
Either way the limo had passed the Lookout at 14.4 sec, & Mr Passenger was 3.6 sec too late & Hoffman was 5.6 sec too late.
No, Hoffman aint never saw no hole in JFK's head.
And, also, don’t forget from a previous reply that Z313 was 26 sec before the Falcon stopped,
hence even if Hoffman looked towards the paling fence carpark as soon as he got out
he would nonetheless be too late to see any paling fence sniper playing toss the rifle.
Hoffman would have looked after JFK & Co for a while, before turning his attention to the east.
Hoffman would at best have seen the early stages of the commotion on & around the triple underpass, but not the first say 30 sec.
And then his attention would return to the remnants of the motorcade straggling past.
By then there would be a crowd at the Lookout -- Hoffman, Mr Passenger, the gawker sitting on the barrier, & say 6 gawkers who had joined them from the queues of cars.
And after about 15 minutes the roadblock would be removed & Hoffman would continue to his dentist. And Hoffman would have a tale to tell.
JFK had been shot, & Hoffman caught a glimpse of the tail of JFK's limo when it was 200 yd north of the rail bridge, ie over 300 yd from Hoffman.