The JFK assassination argument has swung back and forth over the last 47 years, but now conspiracy theorists — seemingly set back in recent years by Warren Commission-endorsing books by Gerald Posner and Vincent Bugliosi — are getting a Hollywood credibility boost from Leonardo DiCaprio. His intention, I mean, to produce and star in a mob-conspiracy flick that’ll be out in 2013 — the 50th anniversary of John F. Kennedy‘s murder.

The film will be called Legacy of Secrecy, and will be based on a respectably reviewed 2009 book called “Legacy of Secrecy: The Long Shadow of the JFK Assassination” by Lamar Waldron and Thom Hartmann.

The book presents evidence that Carlos Marcello, the Don Corleone of Louisiana and most of Texas, confessed to credible FBI-supported informant Jack Van Laningham that he ordered JFK’s assassination. DiCaprio would play Van Laningham, but let’s eliminate any ideas right now of Joe Pesci or anyone too character actor-ish playing Marcello.

Is the conspiracy crowd indeed back with a vengeance and fresh zeal, and have the reputations of Posner’s “Case Closed” and Bugliosi’s “Four Days in November” been diminishing to some extent? I’ve been feeling this, sensing it. And now DiCpario, picking up where Oliver Stone left off, is stepping up with some Hollywood money to help seal the deal.

Two other formidable conspiracy books are James W. Douglass‘s “JFK and the Unspeakable: Why He Died and Why It Matters” and G. Paul Chambers‘ “Head Shot.”