Caro never stated this. Despite the efforts of the conspiracy theorists, what happened is that Lee Harvey Oswald, the LONE gunman assasinated JFK. Where the conspiracty theories find nourishment is that Oswald himself loved to think of himself as part of some espionage network. I knew someone like this so Oswalds delusional thinking is nothing surprising to me. The funny thing is that a lot of folks buy into Oswald's delusions. But enough on oswald, let's get the discussion BACK to Caro and his book.
I think the conspiracy theories also get nourishment from the fact that Oswald couldn't have fired so many bullets from so many different directions in such a small space of time by himself.