Momo started working with the CIA to bring the Kennedys down. He was eager to strike back, but couldn’t use the powerhouse footage he had of Jack’s "indiscretions" as him main shot. The CIA vetoed this idea since the material had been obtained illegally and could backfire against their user. So, according to Chuck Giancana's oft-startling revelations in “Double Cross”, Momo found another way. His object was still to destroy the Kennedy’s good-boy Roman Catholic image. (Bobby had just been named "Family Man of the Year" by a national magazine.) The trysts Momo had been having with movie star Marilyn Monroe had been cooling since he began seeing more and more of Phyllis McGuire. But, they had remained friends and he knew she was sharing her time with other men, including both the married Kennedy brothers. She had recently confessed to him that she had fallen in love with Bobby.

Through his CIA informants who had bugged Marilyn’s phone, Momo learned that Bobby was to be in California on August 4, 1962, and had arranged a rendezvous at Marilyn’s house for that evening. The plan that ensued was diabolical. Momo sent his two most-trusted hit men, "Needles" Gianola and "Mugsy" Tortorella, to case Marilyn’s house and, after Bobby departed, to make their move.

Roselli was to call in her to house, and she would let him in because they were friends. While Roselli and Monroe sat on a white couch and talked, the men slipped into the house from an unlocked window, and snuck up behind her. She understood immediately what was happening. A tall, muscular, woman she fought back against them and they punched her into submission. An autopsy later showed a fresh prominent bruise on Monroe's hip and it was noted in the final report, "There is no explanation for the bruise. It's a sign of violence." While Roselli either continued to beat Monroe, or, hold her down, Spilotro pulled a chloroform-soaked cloth from a plastic bag, and pressed it over Monroe's mouth and nose. If the first dose didn't kill her, they had a thermos filled with highly concentrated mixture of chloral hydrate, Nembutal and water, to make sure the job got done the right way.

After Monroe stopped struggling, they stripped her, placed a towel under her buttocks, dipped a syringe in Vaseline and slid it slowly into her rectum and let the poison go into her colon. A second dose followed, they laid her on the bed, went into her medicine cabinet and lined two dozen bottles of various drugs on her night stand next to her bed. However they failed to leave a glass near the bed and Monroe never took a pill without water. They left her on her bed, face down in her pillow, her arms at her sides, she was perfectly straight.

According to the theory put forth in the book, the executioners would kill the star and make her death look like suicide. Naturally, Momo figured, the Attorney General would be dragged into the case when police discovered the love letters from Bobby that Momo knew she kept; besides this, Marilyn’s housekeeper always answered the door when anyone visited and would be sure under police scrutiny to admit that Kennedy had been there moments before she died. Momo’s press friends were put on alert; they were ordered to make the most of the "tragic, unrequited love affair that sent poor Marilyn racing for the bottle of barbiturates".

August 4...waiting paid off. Bobby arrived at Marilyn’s Palm Springs, California, mansion early evening, let in by the housekeeper. He left Marilyn around midnight. Waiting for her maid to retire, which was soon thereafter, the two killers stole into Marilyn’s bedroom. There, Chuck Giancana insists, they overcame her and inserted a Nembutal suppository into her anus. It was not the first time the device was used; it had eliminated other celebrities who had, when found dead, been written off as suicides. It was untraceable and the drug worked quickly, seeping its poison into the blood stream, appearing as if she had overdosed. Before they left the house, Gianola opened a bottle of pills, poured most of them into his pocket, and sprinkled a few beside her on the bed along with the empty bottle. The housekeeper discovered Marilyn’s corpse the following morning.

Momo envisioned the headlines:

"MARILYN MONROE FOUND DEAD; THE KENNEDYS IMPLICATED."

Kennedys pulled out all stops to censure investigation and keep newspaper reporters at bay. Peter Lawford and FBI agents, on Presidential instruction, removed anything accusatory from the Monroe home. When the coroner pronounced his hearing later in the day he expediently ruled, "Probable suicide". The housekeeper said nothing.

Whether or not the Kennedys suspected Momo was behind Monroe's death is not known, but suddenly FBI agents dogged his footsteps, worse than ever.

Throughout the Outfit it became common knowledge: Momo had been pushed way beyond his limit. He was going to strike big-time against the Kennedy family.

Of the many theories involving who killed President Kennedy and why, Chuck Giancana's "Double Cross" adds a new theory --that it was indeed his brother Momo who perpetrated the national crime. Claiming to have first-hand knowledge, he recalls the night that Momo confessed his involvement to him in the privacy of the latter's Oak Park basement: "He lifted his cigar to his lips and a cruel smile curled like an embrace around it. There was a deadly silence in the room . . . For the next hour (Momo) shared the darkest and most horrifying of his secrets."

On November 22, 1963, in a scene reminiscent of the Anton Cermak killing 30 years earlier, John F. Kennedy, riding in an open-car motorcade through the streets of Dallas, had his head blown open by a sniper. Very few in Mobdom were surprised. And when the hysteria died down, neither was Bobby Kennedy.

Was it Momo who assassinated President Kennedy?