by Gerald Posner, Random House, 607 pages

The conspiracy-book industry seized on last fall’s thirtieth anniversary of the Kennedy tragedy for its latest barrage. Among all the new volumes, Gerald Posner’s calm and definitive study, Case Closed: Lee Harvey Oswald and the Assassination of JFK , arrives at the most truly radical conclusion: “One man, acting alone, killed the President.” He asserts that the Warren Commission’s 1964 report was flawed but correct after all.

The more you know about Oswald, Posner shows, the more inescapable it seems that he was the unassisted killer. As he convincingly demonstrates, the adult Oswald simply wasn’t stable enough to have played a major role in an elaborate farreaching conspiracy that stayed secret. Posner also sets straight the long-debated facts of the Dallas shooting and analyzes the Warren Commission’s investigation. There is a probing chapter on Jack Ruby, an excellent appendix on ballistics, and a fascinating look at the Zapruder film, using computer enhancement to trace the trajectories backward from the bullet wounds. This book’s flimsy predecessors are no match for it.