Oswald was a frustrated man who never got the chances he 'deserved'. His murder of Kennedy was to prove to Marina he was a 'great man.' Nothing more, nothing less. Oswald did it....alone.
Specters theory threw out the 1st shot at an [early] frame in the 160's, as JFK disappeared [to Oswald] in the foliage at frame 166. - Unless it missed, which is contradicted by most all other evidence, namely that it would have had to ricochet over 100 yds downrange to hit the underpass curb.
At frame 166, - Oswald would have had to be standing, - or seated leaning far out of the window, - in order to achieve the steep downward angle to his target, - which was also moving away down the street to the right. Tough shot, which he probably did not take.
We are then left with this sequence:
First shot at frame 210, - 'neck' hit.
Cycle bolt [2.3 seconds] aim, fire, miss. [curb hit?]
Cycle bolt [2.3 seconds] aim, fire, head shot [frame 313].
The shot at frame 210 is still at a fairly steep down angle, with the limo going to Oswalds right, making it even more difficult to line up the single bullet with JFK's wounds - and Connelly's wounds.
Thus, the 3rd shot is the 'easy one' from Oswalds position, with the down angle decreased and the limo going fairly straight away.
All told, the sequence of shots that Specter dreamed up has major flaws. - And has never been duplicated convincingly .
Feel free to draft your own sequence of shots, showing when they were made and what they hit. No one to date can better Specters flawed version.