After days of hearing how the Mafia operates in Italy and New York, the Charbonneau Commission finally began learning how the criminal syndicate performs in Canada and Quebec.

RCMP officer Linda Fequiere described the power shifts between the various clans, and how Project Colisee led to a power vacuum among Montreal's criminal underground.

Construction bosses were regular visitors at a notorious Montreal Mafia hangout several years ago while authorities quietly observed during a police surveillance operation, RCMP Cpl. Vinicio Sebastiano told the inquiry Tuesday.

 In some of those visits, he testified, construction entrepreneurs were seen bringing money to the acting head of the Rizzuto clan -- the late Nicolo Rizzuto Sr. -- or his consigliere, Paolo Renda, who has been missing since 2010.

Rattling off names of well-known construction bosses in the Montreal area, the RCMP officer testified that they often showed up at a now-closed cafe that used to be frequented mainly by Mob types.

Colisee led to the arrest of multiple suspected members of the mafia, including Rizzuto Sr., who was later murdered in his home in November 2010.

Fequiere detailed the bloody rise of the Rizzutos in the late 1970s and early '80s.

She said Vito Rizzuto was able to forge alliances and act as a peacemaker to solidify the clan's power base in Montreal.

Those alliances included Calabrian groups previously tied to the clan deposed by the Rizzutos.

She said he also brokered arrangements with other groups like criminal biker gangs and the Irish Mob.

"Vito Rizzuto worked as a mediator. He was someone who could find solutions when there were problems among different groups," Fequiere said.

But the family fortunes changed.

Its troubles accelerated following Rizzuto's extradition to the United States, where he is serving a jail sentence for a 30-year-old killing, and after Operation Colisee, the largest anti-Mafia police sweep in Canadian history. Numerous family members would up dead or in prison.

Without naming any names, Fequiere said a faction of the Calabrian Mafia -- which held power in Quebec for three decades before the rise of the Rizzutos -- has taken over again.

Fequiere said she wouldn't go into details about who is in charge, noting that investigations could be compromised.

"I'm not saying the Sicilian faction has completely disappeared -- but there is a return of the Calabrian faction that happened after the arrest and extradition of Vito Rizzuto," Fequiere said.

Rizzuto, currently jailed in the U.S., is scheduled to be released in a few weeks.

Fequiere says investigations have shown that Mafia in Montreal focuses on a few traditional staples: the drug trade, sports betting and illegal gambling, extortion, and money laundering as their principal illegitimate money-makers.

They are also involved in numerous legal industries such as restaurants, construction companies and private security, she said. Renda, Vito Rizzuto's brother-in-law, owned a construction company, Fequiere noted.

That lengthy Colisee operation began in 2001 and had as its main goal to destabilize the mob, with a secondary focus on disrupting the importation of contraband drugs.

Officers learned during the course of their investigation, including through wiretaps, of instances of intimidation in the construction industry and corruption of public officials. That information was passed on to the Surete du Quebec.

With a report from The Canadian Press