WASHINGTON -- Conspiracy theorists who question President John F. Kennedy's assassination in 1963 have, over the years, become obsessed with another murder. On Oct. 12, 1964, socialite and artist Mary Pinchot Meyer, a longtime Kennedy mistress, was shot execution-style in broad daylight while walking along the Georgetown canal towpath.

Within hours, police charged day laborer Ray Crump Jr. with murder. They never found the gun, however, and a jury acquitted Crump after an eyewitness described the killer as much bigger than the diminutive defendant. In the ensuing years, the case has become one of Washington's most infamous unresolved murder cases.

In his new book, "Mary's Mosaic: The CIA Conspiracy to Murder John F. Kennedy, Mary Pinchot Meyer, and Their Vision of World Peace," author Peter Janney lays out a complex web of high society and high crimes that implicates some of the nation's most respected intelligence agents, journalists and government officials in what Janney contends was a massive cover-up spanning three decades. At the center is a shadowy, all-too-familiar villain, the Central Intelligence Agency of the early-1960s.

Meyer was born into a wealthy Pennsylvania family in 1920, and first met Kennedy at a prep school dance in 1938. She attended Vassar College and married CIA agent Cord Meyer in 1944. By the mid-1950s, the couple was firmly established as part of Georgetown's glittering young social set, whose members included then-Sen. Kennedy and his wife, Jackie; Washington Post publisher Phil Graham and his wife, Katherine; and journalist Joseph Alsop. The Meyers divorced in 1958, when Mary was 38.

After Kennedy's election as president, Meyer became a frequent visitor to the White House, and her sexual relationship with the president was well known at the time, according to Janney and previous accounts, notably a 1998 biography of Meyer by journalist Nina Burleigh titled "A Very Private Woman: The Life and Unsolved Murder of Presidential Mistress Mary Meyer."

Less well known was Meyer's friendship with then-Harvard professor and LSD guru Timothy Leary, whom she visited several times at his office in Cambridge, Mass. Janney's book contains the most exhaustive account to date of Meyer's communication with Leary, who died in 1996. Much of Janney's account is based on interviews Leary gave to another Kennedy conspiracy enthusiast, the investigative journalist and author Leo Damore. Damore had been doing research for a book about Meyer before he committed suicide in 1995. In 2004, Janney purchased Damore's notes and audio recordings on the Meyer case from his estate.

Janney's principal thesis is that Meyer and Kennedy were deeply in love and experimented with drugs together. Partly as a result of his relationship with Meyer, an avowed pacifist, Kennedy began to question the American military buildup that characterized the Cold War, according to Janney.

Like others before him, Janney posits that Kennedy's assassination was the result of a CIA plot to eliminate the only man in the way of the agency's total control over U.S. foreign policy. Those same forces, Janney argues, viewed Meyer, an intimate confidante of the late president, as a similar threat.

"Understandably preoccupied with Jack’s assassination, she maintained a collection of 'clippings of the JFK assassination' in the bookcase in her bedroom, next to the place where she kept her diary," Janney writes. "The lingering question was how far Mary had gone in her investigation, and what impact it might have had."

Janney's theory is that an Army lieutenant and suspected CIA hit man named William Mitchell shot Meyer. The author says this hypothesis is strengthened by the fact that neither the U.S. military nor Georgetown University, where Mitchell said he was a professor, have any record of him. Damore claimed to have spoken on the phone with Mitchell in 1993, and told his lawyer that Mitchell confessed to him that Meyer's murder was "standard CIA procedure."

It's unclear why Damore didn't come forward with this revelation before taking his own life. Perhaps he was saving it to use in his never-published book. Mitchell has never been located.

Also missing from the history books is a diary that Meyer is said to have kept, which her brother-in-law at the time, Washington Post editor Ben Bradlee, sought to retrieve sometime in the 24 hours after her death. Bradlee said the diary contained mostly sketches, but Janney said he believes it held a detailed account of her affair with Kennedy, and may have revealed who might have wanted her killed.

There are conflicting accounts of what happened to the diary. Meyer's sister, Tony Bradlee, said she burned it. Damore claimed to have located a copy. There are questionable secondhand accounts claiming it was turned over to CIA spymaster James Angleton.

Janney suggests that Bradlee helped cover up his sister-in-law's murder in order to advance his career, writing that Bradlee "played fast and loose with the facts" surrounding Meyer's death.

Like all great conspiracy theories, Janney's account requires readers to make a certain leap of faith. There is no direct evidence of illegal drug use by Kennedy, yet Janney spends a significant portion of the book exploring possible scenarios and it's clear he thinks hallucinogens had an effect upon Kennedy's outlook. There is equally little evidence that Ben Bradlee did anything wrong, other than perhaps misremembering the exact sequence of events that happened almost 40 years ago. Moreover, key characters have never been located, including Janney's suspected triggerman, Mitchell.

Therein lies the problem. Janney's account leaves ample suspicion, even doubt, about the events surrounding the deaths of both Kennedy and Meyer. But all too often, Janney fills in blanks with conclusions that forward his preconceived narrative.

"Mary's Mosaic" is an entertaining trip through the dark possibilities of Washington's covert history. Janney's research gives enthusiasts of Kennedy lore, along with fans of Cold War spy tales, much to consider. But despite his unified theory of how it all went down, Janney's book is unlikely to put lingering questions about Meyer's death to rest.