Convicted Montreal crime boss Nicolo Rizzuto leaves a Montreal prison on Thursday. (Graham Hughes/Canadian Press)

Nicolo Rizzuto, the presumed patriarch of Montreal's Mafia, has been given a suspended sentence and probation after previously pleading guilty to two criminal charges.

Rizzuto, 84, who goes by the first name Nick, pleaded guilty to gangsterism-related charges in September along with five of his associates, after striking a plea bargain with Crown prosecutors earlier this year.

He was freed from prison Thursday evening.

The six men were among dozens targeted by a large-scale sting operation in 2006 that aimed at the underbelly of Montreal's Mafia underworld.

The Crown acknowledged Thursday that police did not do a thorough job of following the money trail in their investigation of Rizzuto, father of alleged Mafia kingpin Vito Rizzuto, and several others.

Despite more than a million hours of wiretap evidence collected by police during the sting operation, known as Operation Colisée, prosecutors could not directly implicate Rizzuto in crimes exposed by investigators.

Crown prosecutor Yvan Poulin said evidence gathered by the RCMP during a four-year investigation showed Nicolo Rizzuto possessed an unknown amount of proceeds of crime.

"The investigation doesn't show what is the specific source of the money he received," he told reporters at the Montreal courthouse. "That was a serious obstacle to the prosecution."

They also took into consideration the limited role he played in the organization, which was involved in importing and exporting drugs through Pierre Elliott Trudeau International Airport in Montreal.

A total of $4 million was seized during the 2006 police operation, but Poulin said no money was confiscated at Rizzuto's home.

Rizzuto eventually pleaded guilty to possession of proceeds of a crime, and possession of the proceeds of crime for the benefit of, the direction of, or in association with a criminal organization.

He will be on probation for three years after being sentenced in Montreal on Thursday.

The suggested sentence for Rizzuto was four years, but since he's already been in custody for two years, both the Crown and defence lawyers recommended a suspended sentence and three years probation.

Rizzuto suffers from age-related health problems, including incontinence and respiratory problems, and would have a hard time in prison, his lawyer argued Thursday.

Rizzuto's five associates — Francesco Arcadi, 55, Francesco Del Balso, 38, Paolo Renda, 69, Rocco Sollecito, 60 and Lorenzo Giordano, 43 — pleaded guilty to an assorted series of charges, including conspiracy to import and export narcotics, drug trafficking, bookmaking, operating illegal gaming houses, gangsterism and extortion.

Arcadi, Del Balso, Renda, Sollecito and Giordano all face sentences from six to 15 years.

With files from the Canadian Press