A professional assassin would only need 1 shot,
You know this, how? Experience or simply watching too many movies?
Btw, does this mean that all those expert rifle men who tried (and failed) to copy what Oswald is supposed to have done were amateurs?
In the 1967 CBS-News re-enactment, Howard Donahue said he was given a Carcano rifle he was unfamiliar with and allowed only three practice shots in a basement firing range before going out to the re-enactment scene.
"CBS News directors apparently believed that if any of
the riflemen had a chance to practice, the results of the
demonstration would be worthless."
-- Mortal Error, 1992, p. 8
They had to shoot at a moving target that represented the limousine, with stakes defining the area in which they could fire. Donahue described the shooting platform as top heavy and exposed to weather.
"A light rain began to fall and the tower swayed slightly
in the wind."
-- Mortal Error, 1992, p. 9
They had to recreate a three-shot scenario, not randomly decide on their own when to aim for the head for a one-shot kill. The marksmen were allowed three attempts each; Donahue seems to be increasingly familiar with the bolt action on each attempt, describing his third:
"Donahue's shots had all hit within a three-inch circle on
the target's head."
-- Mortal Error, 1992, p. 9