Honestly, I saw many movies/documentaries on that subject and I seriously beleive the conspiracy theory.
- Some calculs concerning the number of rounds fired VS. the time of the shooting proved that the "operation" needed at least two snipers.
- When you looks at the bullets' trajectory you see that there was a sniper in a building, an other one behind a wall/tree (can't remember exactly) and a third one somewhere else (they told where in a documentary, but I don't remember).
- The guy who replaced JFK took an oath barely two hours after the shooting... It happened in the plane carrying JFK's coffin. A picture was taken of the ceremony. We could see the new president, his wife, Jackie Kennedy, and a body-guard of JFK. Don't you think all that happened a bit in a hurry ?
If you watch the movie Kevin Costner made on this subject and compare it to the National Geographic's documentary, you'll see that what he made was not far from the reality. But did Oswald shot at him or not ? We'll never know. What we are sure of is that it needed more than a single sniper. And what's make it looks more weird is that the new President was named very fast.
My personnal conclusion ? There was a conspiracy from the CIA led by JFK's successor himself.
But who am I to judge ? I'm only a little Security Officer/Private Investigator.