On June 20, 1975, Weldon Whisler’s phone rang at 1 in the morning. Instead of rolling over and going back to sleep, he answered it. That is the mark of a journeyman reporter.

“Have you got a paper and pencil handy?” the caller asked. “I’m going home now and to bed, and I will not answer the telephone; no one else will get the information I am giving you for several hours.”

Oak Park police had responded to a call for assistance by the crew of Fire Department ambulance 613 at 1147 S. Wenonah Ave. The address might have rung a bell for an old pro like Whisler, who got there so quickly that his account in the morning’s Tribune corresponded perfectly with Police Report 75-761. Other news outlets were left scrambling to catch up.

“Gangland boss Sam (Momo) Giancana was found shot to death on the floor of his basement kitchen early Friday morning, Oak Park Police said,” Weldon wrote. “The onetime chief of the Chicago syndicate was found lying face up with four or five bullet wounds in his head, police said. Six .22 caliber bullets were lying around the body.”

The police report noted that “a frying pan on the right rear burner of the stove that was to the right of the victim contained food that was still warm.”

It looked like he’d been frying up a late-night snack before someone shot him. He had been on a restricted diet, recovering from gall bladder surgery. Francine, his youngest daughter, brought him the ingredients of his favorite dish: sausage, escarole, and ceci beans.

About 10 p.m., a squad of Chicago police officers keeping Giancana under surveillance saw some guests, who were apparently at the house to welcome him home from a Houston hospital, leave. Joe DiPersio, Momo’s caretaker, went upstairs, having told his boss to call if he needed anything.

Thirty minutes later, DiPersio came downstairs to check on Giancana. Someone had either arrived, or doubled back. Giancana was lying in a pool of blood in the basement kitchen.

DiPersilio and his wife told the cops they didn’t hear any shots. When the police asked if the basement door was locked, DiPersilio replied that the door was never locked.

Nothing was missing from Giancana’s elegantly furnished home. His wallet was found near his body, and a money clip holding more than $1,458 was in his pocket, the Tribune reported. So it seemed the killer’s only motive was to to seal the victim’s lips before he blabbed about something that someone didn’t want to be publicly known.

The generally accepted theory on Giancana’s murder is that he was killed by one of his Outfit cronies to keep him quiet. Giancana was scheduled to testify before the Church Committee, a congressional investigation of rumored links between the CIA and gangsters.

Giancana had risen from a juvenile delinquent to the Outfit’s upper echelon. As an adolescent, Giancana belonged to a Taylor Street gang that took its name from the story “Ali Baba and the 40 Thieves.” Thinking themselves even better thieves, they dubbed their gang “The 42.”

Graduating into the mob, he earned his spurs by making Theodore Roe an offer he couldn’t refuse. Roe, an African American mobster, ran a policy wheel that offered prize money to players who picked the right sequence of random numbers.

He kidnapped Roe and demanded a $100,000 ransom. It was paid, but Roe refused to surrender his business. On Aug. 4, 1952, Roe was shot to death while sitting outside his South Michigan Avenue mansion.

In 1965, Giancana was subpoenaed by a federal grand jury. Despite a grant of immunity, he refused to answer questions, citing the Fifth Amendment. He was convicted of contempt and served a year in prison. Hoping to lie low, he fled to Mexico. But the U.S. pressured Mexican officials to deport him, and in 1974, he was back in town.

William Roemer, an FBI agent who made his name fighting the mob, was shocked when he saw Giancana arrive back in Chicago from Mexico.

“He was undoubtedly the wealthiest person on the plane, but he looked like some Italian immigrant landing at Ellis Island, destitute and frail,” recalled Roemer.

Theories about his assassination fall into two groups. One is local and sees his death in the context of mob practices. A wide-angle view places Momo in the context of international affairs.

The latter turns on the government’s fear that Fidel Castro had given communism a New World foothold in Cuba. President John Kennedy hoped to get rid of Castro by a double-barreled means: an invasion by Castro’s exiled opponents, accompanied by his murder. The plot’s details were subsequently revealed in the CIA’s self-study of questionable tactics.

The CIA needed someone experienced in quietly getting rid of enemies. Momo’s rap sheet matched the job description. Could his murder be Castro’s payback for signing on to a planned assassination of the Cuban dictator?

The case remains unsolved.

Giancana’s nickname “Momo” was shorthand for Mooney, or madman. “He has a constitutional psychopathic state,” a draft board found in 1943. “He has an inadequate personality and strong anti-social trends.”

He’d told the board he made his living stealing: “They thought I was crazy. But I wasn’t. I was telling the truth.”

Ron Grossman is a columnist emeritus for the Chicago Tribune. His columns vary from social and political commentary to chapters in Chicago history. Before turning to journalism, Grossman was a history professor. He is the author of “Guide to Chicago Neighborhoods.”