JFK conspiracy: Any smoking gun besides Oswald's?

(CBS News)   A little more than ten months after the assassination, a commission headed by Chief Justice Earl Warren issued its report -- and what it concluded fell far short of satisfying those who believe there must be more to the story. Tracy Smith has been looking into that:

Sunday, September 27, 1964, 6:30 p.m. Eastern time. Fifteen seconds after the Warren Commission Report went public, CBS News anchor Walter Cronkite summed it up:

"Who killed John F. Kennedy? The commission answers unequivocally Lee Harvey Oswald. Did Oswald act alone or was he a member of a conspiracy? The commission answers he acted alone."

But even at that time, most Americans had their doubts.

In a 1963 Gallup poll, when asked if some group or element was also responsible for the killing, more than half of U.S. adults said yes -- and those numbers would grow over time.

In the absence of official information, rumors took root: the most common were that the mob was behind it, or the CIA, or Fidel Castro.

Just this year, former New York Times reporter Philip Shenon revealed that the Warren Commission went so far as to send a man to question Castro face-to-face. In a clandestine meeting on a boat off the Cuban coast, Castro denied any part in the assassination.

Still, the conspiracy theories piled up: Oswald, with his cheap little rifle, couldn't have done it alone.

An unending parade of investigators and news outlets (not the least of which was CBS News) spent years and whatever money it took to find evidence -- ANY evidence -- that the official story wasn't the whole story.

In the 1970s, the House Select Committee on Assassinations confirmed Oswald's involvement, but left the door open for the possibility of another gunman.

The conspiracy theory has been kept alive by other revelations over the years, like a reported plot to kill Kennedy in Chicago three weeks before Dallas.

But few things fueled Americans' belief in a conspiracy more than director Oliver Stone's 1991 film, "JFK."

Stone made what might be the best-known case against the Warren Commission Report.

Twenty-two years later, Stone is still convinced.

"Look, don't kid yourself: governments lie," he told Smith.

"Do you see conspiracies in everything? Asked Smith.

"No, not in everything," said Stone. "We have conspiracies, but we also have actions that happen randomly, and accidents do happen."

"Could it just be that we can't wrap our minds around the idea that the most powerful man in the world could be taken out by a nobody?" Smith asked.