The front-yard execution of a skilled Mafia diplomat who survived decades in the top echelons of the Montreal mob may mark the end of a war - or it may be the start of the final battle for control.

Giuseppe "Joe" Di Maulo, who came up in the mob in the 1960s, survived the purge of his Calabrian bosses in the late 1970s and early 1980s, and hung on as most of the Rizzuto clan was jailed or killed through the 2000s, was shot dead in his driveway Sunday evening. Mr. Di Maulo's body was left to be discovered by his wife outside their home in Blainville, a bedroom community 45 minutes north of Montreal. He was 72.

The death of a man who built a career sliding easily among the top ranks of the Calabrian and Sicilian regimes that have long ruled Canada's mob comes within a month of the return to Montreal of Vito Rizzuto, the last don of the high-profile family that most recently ruled the city.

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Mr. Rizzuto was released last month after serving a five-year prison term in the United States. In his absence, his father and a son (both known as Nick Rizzuto) were murdered and most of his top associates were gunned down or disappeared. Mr. Di Maulo's death also occurred as the Rizzuto infiltration into the construction business faces a new level of public scrutiny in the Charbonneau corruption inquiry.

The killing led quickly to two preferred theories among Quebec's organized crime experts, and Mr. Rizzuto is at the centre of both: The Montreal godfather is either emphatically trying to regain control of his territory, or having authority exercised upon him.

"Vito Rizzuto gets out, and this immediately happens. If it's a coincidence, it would be a very strange one," said Pierre de Champlain, a former RCMP intelligence analyst and author. "[Di Maulo] was an iconic figure among the Mafia in Montreal, and he was legendary for his discretion. He partly gained prestige and influence because his name so rarely came up."

Mr. Di Maulo is described as being "blessed with an undeniable talent for diplomacy" in Mafia Inc., the latest, authoritative book on the Montreal mob, and his complicated history makes it difficult to be certain if he died a Rizzuto enemy, or friend.

In the 1970s, the rising Sicilian clan went to war against the Calabrian Catronis and eliminated a brash new-generation leader, Paolo Violi. Mr. Di Maulo made it from the Catronis to Mr. Violi and his brothers, only to land as a trusted lieutenant of the Rizzutos.

Most recently, he was linked to a failed attempt to consolidate control with Salvatore "The Ironworker" Montagna and Raynald Desjardins, one of the rare francophone Quebeckers to rise in the mob ranks. The alliance evidently fell apart. Mr. Montagna was gunned down last year, and Mr. Desjardins (Mr. Di Maulo's brother-in-law) awaits trial accused of the murder.

As RCMP mob intelligence analyst Linda Féquière noted in her recent testimony at the Charbonneau commission, Mr. Di Maulo was always most closely identified as a member of the Cotroni-Violi Calabrian wing of the mob.

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Mr. Di Maulo died much as former godfather Nicolo Rizzuto did exactly two years ago: at home, by bullet, with his wife nearby to tend to the body. It's unusually intimate for mobsters, who generally try to keep such business away from wives and children.

But echoes of the method go back to the last war, in 1980, when Rocco Violi was shot through a window by high-powered rifle while sitting at the dinner table with his family. Mr. Violi's wives and children moved to Hamilton, where they lived under the protection of a Calbrian mob family, according to André Cédilot and André Noël, the authors of Mafia Inc.

Every member of the Rizzuto organization who was picked up for questioning in the Violi murders from more than 30 years ago has now been killed – most of them in the past three years, Mr. de Champlain said.

"I was never a fan of the revenge theory, but as time passes it starts to seem increasingly possible that revenge is behind this," Mr. de Champlain said. "And you know what they say about revenge being best served cold."

With a report from Tu Thanh Ha

Editor's note: An earlier version of this article included an incorrect spelling of one of the families involved. This online version has been corrected.