Case Closed: Lee Harvey Oswald and the Assassination of JFK.

Case Closed: Lee Harvey Oswald and the Assassination of JFK, by Gerald Posner (Random House, 607 pp., $25)

THIS is the book on the JFK assassination, the definitive work that cuts through all the confusion and misinformation. Posner builds an overwhelming evidentiary case that Lee Oswald was the lone assassin, just as the Warren Commission concluded. Using up-to-date computer enhancement of the Zapruder film to determine the number and timing of the shots, Posner explains how the single-bullet theory is not only possible but unavoidable. He faults the FBI and CIA for their clumsy efforts to conceal their own embarrassment over Oswald, whom they should have kept an eye on--but finds no mega-conspiracy beyond that. One of the strongest and most important features of the book, indeed, is Posner's painstaking dissection of each and every one of the competing conspiracy theories. None of them stands up under scrutiny. We can be certain, unfortunately, that this tour de force will be dismissed in some quarters as just another phase of the conspiracy. The mountain of new files being released these days by the National Archives, including FBI and CIA materials, will probably only encourage the nitpickers to sow confusion with what has been released and continue to shout "coverup" because some intelligence materials are still withheld. But for the non-hysterical, this book will be the end of the debate.