[Dirty Meg]

A secret US security force (under the command of the real president) killed Kennedy because of embarrassing concessions made to the Soviet union over all that Cuban missle bollocks, and because he repeatedly risked starting a nuclear war. (If the assassination attempts on Castro had succeeded, there may have been nuclear war. Before WWI, two super-powers built up their armies, thinking that the risk of a hugely destructive war would be an effective deterent. There is no reason to assume that the same plan which failed to prevent WWI would prevent WWIII).
However, there was only one gunman involved in the Kennedy assassination. No secret organisation would employ two gunmen, risking exposure if both were caught, when one could do the job. The second gunman theory was invented by the same organisation that employed Oswald to kill Kennedy.