They wanted two co-ordinated volleys of shots at Kennedy to insure a kill. The link describes the sequence.
“They wanted two co-ordinated volleys of shots at Kennedy to insure a kill”
Why bother? The Book Depository provided a perfect shot, with the car moving straight away from the shooter at a gradual downward slope. Already basically a stationary target. Much simpler than coordinated volleys and paralyzing darts shot from umbrellas.