Who killed Momo? NBC 5 investigates Chicago mob boss Sam Giancana murder mystery

"Who killed Momo" is the Chicago Outfit's last family secret.

NBC 5 Investigates dug into a case that has been dormant and gathering dust. We spoke with men once on the inside of the mob and those who have examined the Sam Giancana assassination from the outside. We've scoured law enforcement files, photos and lab reports, and we've interviewed police, prosecutors and mob figures to determine who pulled off Chicago's greatest hit. 

There have been more than 1,400 mob murders in Chicago since the Roaring 20s.

Nearly all of them have gone unsolved.

Officially that number incudes the killing of villainous Outfit legend Giancana. His mob moniker "Momo" is short for Mooney, aka crazy.

"Giancana was a very influential person in the Outfit," said Douglas Depodesta, special-agent-in-charge of the FBI Chicago.

"He led the Outfit from the late '50s to the middle '70s. He was dating one of the McGuire sisters. He hung out with the Rat Pack. So of course there was a lot of attention at the time," said DePodesta.

Fifty years ago, in spring 1975, Momo was in his west suburban Oak Park home, living in a basement apartment. Police photos of Giancana's actual abode -- and what would become the crime scene -- have never been shown publicly until now. 

There are framed illustrations of circus clowns adorning his office wall and a stand-up ashtray on scene, the depository for his cigar butts. And there is this hardline house phone, where 67-year-old Giancana conducted crime syndicate business.

He had just returned from gall bladder surgery in Houston, and a few friends were over to welcome him home.

One photo shows how Chicago police detectives had the gangster's bungalow under surveillance, confirmed by a police report we obtained. But NBC Chicago sources say what isn't in the report is that when Giancana's guests left, so did CPD intelligence officers -- into the dead of night.

Before 11 p.m. there was a visitor, someone Giancana apparently trusted enough to allow in through a basement stairwell.

The hoodlum started making a late-night snack. Giancana was standing over this frying pan, sizzling sausage and escarole with beans, when his houseguest fired one shot from this silencer-equipped 22-caliber pistol right into to the back of Giancana's head. And then after the mobster collapsed, six more shots into his mouth, symbolizing the Outfit’s golden rule: Thou shall not talk.

"Whoever it was, was professional enough to know that they wanted to make sure he did not survive," said reformed Chicago mobster Frank Calabrese, Jr.

Calabrese, Jr. has mob DNA in his blood. His dad Frank "the Breeze" Calabrese, Sr. was a Chicago crime boss and an Outfit hitman.

In 1975, with Giancana under subpoena to testify before the U.S Senate Intelligence Committee, some syndicate insiders may have been jittery about whether he was going to break his vow of omerta, or secrecy, and say too much about ties between the mob and the Central Intelligence Agency. Motive enough for murder.

"The world of the Chicago Outfit and organized crime is a dirty, nasty little world," stated mobologist John Binder, who said there were numerous murder suspects in the mob hit 50 years ago, but never enough evidence to prosecute.

"There's various claims about different people, credible claims to some extent, more or less about who might have killed Giancana," said Binder, who authored a 2003 book on the mob, "The Chicago Outfit."

"I think the most likely version of events is it was Butch Blasi," said Binder. "He was there that night. There was a little party at Giancana's house. Included were two Outfit guys: Blasi and Chuck English."

Chuckie English was a Chicago Outfit rackets boss, who himself would be murdered a decade later. He was never charged and neither was Dominic "Butch" Blasi, Giancana's longtime bodyguard and wheelman.

Across the country, at The Mob Museum in Las Vegas, where Sam Giancana is a prominent face on the wall, Outfit expert Jeff Schumacher said Momo's death confounded detectives from Day One.  

"There are suspects. There are theories. But you know, at this point in time, it's going to be pretty tough," said Schumacher, vice president of museum exhibits and programs.

In Part Two of "Who Killed Momo," we go inside the Giancana police files. NBC Chicago will revisit the evidence, trace the gun, look into who showed up in the dead of night and reveal the name of the man who did it.

Who pulled the trigger? And why will that man never be charged?