Assuming Oswald makes the relatively simple shot...
-7 for the skull.
+4 for Acc for aiming.
+1 for braced.
40 yards for the first shot, (-10 for elevation) effectively 30. -7 for range.
The 20 yards per second speed of the limo adds to the range making it 50 yards, effectively, and -8 to hit.
-10 to hit, this is the shot that missed! He'd need a skill of, at least, 13 to get a roll at all.
70 yards for the second shot. 90 for the third. Very little lateral movement from vehicle speed.
-9 for the second shot and -10 for the third.
-7 to hit the skull.
+4 for Acc for aiming.
+1 for braced.
-11 for the second shot, -12 for the third.
To get a roll at all for the third shot, Oswald has to have a skill of, at least, 15.
I've statted myself at 16 from measuring my groups and accounting for all the variables and I don't think of myself as an awesome shot...
I've seen players roll statistically unlikely rolls in the game before, so a skill of 18 and a rolls of 9+, 7- and 6- in a row is plausible.
5d pi to the neck/body. No DR. 10 HP. Avg damage roll will be 17.5 points, or 17. Possible damage ranges from 5 to 30 points.
10 HP done to Kennedy, 7 continues to Connally.
Hit to the body. If average hit, wrist cannot be struck.
Normally the rules don't allow for the wrist to be struck either, but we can extrapolate...
It would take 3 points of damage to cripple a hand. That means Connally had to have taken 13 points of damage and Kennedy 23.
Using both the Bleeding rules from B420 and the Body Hits rules from High Tech 162, the first shot only does 10 points of damage to Kennedy and 13 to Connally.
Both people hit appear to have made their consciousness rolls.
5d pi to the skull. DR 2 from the bone. An average, 17 point, hit will get 15 points to penetrate and is quadrupled for 60. Auto death.
The Kennedy assassination GURPS.
Update: Simple math mistake fixed and the effects of that changed. 4 x 15 is NOT 30. DURRRR.