The evidence-based judge and the professional conspiracy theorist agreed to disagree on the JFK assassination on Tuesday.

On the 48th anniversary of the death of President John F. Kennedy in Dallas, U.S. District Court Judge John Tunheim and former Gov. Jesse Ventura -- host of a TV show and author of books devoted to conspiracy theories -- chewed over the evidence and the many unanswered questions.

"I see a lot of shades of gray," said Tunheim, who became an expert in the JFK story while chairing a board that reviewed government assassination records. He said the evidence supports Lee Harvey Oswald as the man who fired the shots but does not preclude theories that he conspired with others.

Ventura questioned how Oswald could have fired all the shots, said he believes a U.S. government conspiracy was behind the assassination and that Oswald was a "government intelligence agent."

"What can we believe in if the truth is a lie?" Ventura asked. "If our country is based upon a lie, the lie that a coup d'etat took place that day, that we ourselves killed our own president, you could understand why it was covered up, because it would destroy the American Dream, wouldn't it, to know that we assassinated our own president."

The men appeared at a forum called "Who Killed President Kennedy? A Review of the Evidence," at the University of Minnesota's Humphrey School of Public Affairs.

Tunheim served as chairman of the U.S. Assassination Records Review Board, which was responsible for reviewing classified assassination documents to determine which should become public. Ventura, Minnesota's governor from 1999 to 2003, is a lifelong JFK conspiracy buff who discussed the event in an audience with Cuban leader Fidel Castro during a visit to Havana. He now hosts "Conspiracy Theory" on cable TV.

Tunheim allowed there is much for theorists to go on, including the weakness of the original police investigation in Dallas; the documented extra-legal activities of the CIA during the 1960s; Oswald's connection to the Soviet Union and to Castro, including embassy visits in Mexico City six weeks before the assassination; the relationship of Jack Ruby, the man who killed Oswald, to organized crime; and a congressional committee's 1979 conclusion, based on audio evidence, that there likely was a second shooter and a conspiracy.

Tunheim discussed the evidence that there was another shooter at the so-called "grassy knoll," which some witnesses suspected. He said the location was "perfect for an ambush" with a picket fence at the top of the knoll and wooded areas and railroad yards in the rear that would have provided an escape route. He said one person wearing a police uniform was seen up in the area that day but was never identified. No spent shells were ever found in the area, and three people arrested with Oswald were released and "not investigated further," Tunheim said.

Ventura said was influenced by the fact that, in a demonstration for his TV program, he attempted the shots Oswald is believed to have made, and was unsuccessful. He said he believes bullets were coming from three different locations. He suggested that Oswald's tax return, if made public, may reveal that he was a government agent. He accused the government and "mainstream media" of participating in a half-century coverup of what really happened.

Referring to U.S. efforts to kill Castro, Ventura said, "Why are we surprised when terrorists attack us, when we've been practicing terrorism for 50 years? Only we call it foreign policy."

Tunheim told the gathering that even at this distance from the event, there is much to chew on. He encouraged Americans to study the evidence and draw their own conclusions.