Of "the usual suspects" (i.e. the mob, the CIA, Cuban dissidents and LBJ) which had the ability to give any or all others orders? Bearing in mind that even the VP has (far) less authority over the CIA than the victim. Even neglect would not explain why the CIA failed to nail serial killers targeting the highest levels of US government, and if it is unlikely the mob could pull off that many hits without the CIA discovering their involvement (if only after the fact) it is COMPLETELY impossible to imagine the same could be achieved by Cuban dissidents up to their ears in the CIA.

Hoover is really the sole plausible alternative to a CIA hit, either directly or through Cuban or mob intermediaries. He not only despised all the Kennedies and viewed RFK in particular as an interloping young punk, he hated MLK every bit as much. But, while Hoover was still going strong at the time of Chappaquiddick, he had been dead nearly two weeks when Wallace was shot.

shrugs Either one believes that a SERIES of "lone" gunmen EACH decided to murder FIVE leading US political figures in under a decade, and succeeded in all but the ONE case where the victim lacked tight Secret Service protection, or there was a broad high level conspiracy. In this case, the number, nature and brief span of the murders (ironically) makes that conspiracy is what satisfies Occams Razor. That many things going that badly wrong that many times in that short a span is NOT the "simplest" solution. Put another way:

We cannot blame a "lone" gunman when there were FIVE of them.