LOS ANGELES, May 13 — The prosecutor who put Charles Manson behind bars now wants to solve another crime — a really simple one, he insists. So simple that it takes only 1,612 pages to prove his case.

Vincent Bugliosi, whose prosecution of Charles Manson in 1970 led him to write one of the best-selling true-crime books of all time, “Helter Skelter,” has now turned his attention to the assassination of President John F. Kennedy.

And that is his full attention: 20 years of research, more than one million words, hundreds of interviews, thousands of documents and more than 10,000 citations. The result, “Reclaiming History: The Assassination of President John F. Kennedy” (W. W. Norton), is due out tomorrow. His conclusion: Lee Harvey Oswald killed Kennedy, and acted alone.

Why would such a simple conclusion require so much argument?

“Because of the unceasing and fanatical obsession of thousands of researchers over the last 43 years, from around the world but mostly in the United States,” Mr. Bugliosi said in an interview at the cafe of the Sportsmen’s Lodge Hotel in Studio City, Calif. “Examining under a high-powered microscope every comma, every period, every detail on every conceivable issue, and making hundreds and hundreds of allegations, they have transformed this simple case into its present form.”