47 years of conspiracy theories have been based on "proving" that Oswald could not have been the lone gunman, and inferring a conspiracy from that. Proving that Oswald was the only shooter does not eliminate the possibility of a conspiracy; there's just the inconvenient lack of evidence of a conspiracy.
I could believe that my computer is run by magic pixies that translate my keyboard input to the screen and scurry off to post my message to FR. You could sit down with me and patiently explain all the electronics involved, and I could be wholly satisfied that they explain the phenomenon. That still does not prove that there are no magic pixies.
Whatever the case, we know the results of what appears as a 'shadow war' going on for power at it's highest levels.