I became all but completely convinced that the Kennedys were involved in Marilyn's death -- and may have even murdered her -- after reading the definitive Marilyn bio Goddess. From the review posted by Amazon.com:
Of the new material presented, the most provocative is Summers's assertion that Monroe's corpse was first discovered by Robert Kennedy and Peter Lawford. The reason for the confusion of facts about her death, says Summers, is that a coverup was conducted to hide Monroe's sexual involvement with both John and Robert Kennedy.
Now we learn that an FBI document implicates both Lawford and RFK in a conspiracy to get rid of the troublesome starlet.
Critically, [the report] raises an alleged conspiracy, apparently overseen by Lawford, for Monroe to unwittingly commit suicide with the drug Seconal, a barbiturate used to treat insomnia and relieve anxiety. The document gives no precise reason why she would be killed but hints it may be linked to her threats to make public her affair with Kennedy, as other conspiracy theories have previously claimed. It states in part: "Peter Lawford, [censored words blacked out] knew from Marilyn's friends that she often made suicide attempts and that she was inclined to fake a suicide attempt in order to arouse sympathy.
"Lawford is reported as having made 'special arrangements' with Marilyn's psychiatrist, Dr Ralph Greenson, from Beverley Hills. The psychiatrist was treating Marilyn for emotional problems and getting her off the use of barbiturates. On her last visit to him he prescribed Seconal tablets and gave her a prescription for 60 of them, which was unusual in quantity especially since he saw her frequently. On the date of her death … her housekeeper put the bottle of pills on the night table. It is reported that the housekeeper and Marilyn's personal secretary and press agent, Pat Newcomb, were co-operating in the plan to induce suicide."
It goes on to say that on the same day, Kennedy had booked out of the Beverley Hills Hotel and flown to San Francisco where he booked into the St Charles Hotel, owned by a friend. "Robert Kennedy made a telephone call from St Charles Hotel, San Francisco, to Peter Lawford to find out if Marilyn was dead yet."
Lawford called and spoke to Monroe "then checked again later to make sure she did not answer". The document claims the housekeeper, Eunice Murray, who had been hired by the actress on the advice of Dr Greenson, then called the psychiatrist.
"Marilyn expected to have her stomach pumped out and get sympathy for her suicide attempt. The psychiatrist left word for Marilyn to take a drive in the fresh air but did not come to see her until after she was known to be dead."
Add that to the giant pile of skeletons tumbling out of the closet this week.
Note: Goddess appears to be out of print, but some used copies are available through the bookstore.