Was there anyone who helped Lee Harvey Oswald kill John F Kennedy?

Not that anyone knows and has been able to prove. Some people pick out someone they don't like, such as Vice President Johnson, or Castro, or gays, or the Mafia, and simply claim they were involved.

But it was a one-man sized job. Oswald bought the rifle by mail order, as legal as church on Sunday then, and there is no reason to believe that the rifle was paid for by someone else, long before JFK's trip to Dallas was planned. It was a cheap but effective and accurate weapon, with a higher muzzle velocity than American military rifles.

For a while people thought there was a second assassin on the grassy knoll. However, the audio "proof" of this, turned out to have been recorded after the assassination. The supposed "Badgeman" assassin, would have had a head the size of an apple, if there had really been anyone there. Turned out to be light and shadow, sunlight glinting off a pop bottle clearly photographed there instants later. In any case, there was a concrete wall between the position, and Kennedy's head, at the crucial instant. The bone beveling where Oswald's bullet struck his skull, proved the shot to have been from behind. The reaction to this, brain matter spraying forward and to the right, caused an initially confusing movement back and to the left. However, had there been a shot from the knoll, it would have exited the left side of the skull, which didn't happen.