Evidence at the crime scene indicates that a gunshot through a backyard window of Nicolo Rizzuto's home brought down the Mafia don who once lorded over an underworld organization with powerful international ties. (Peter Ray Rakobowchuk/Canadian Press)The funeral for slain Mafia patriarch Nicolo Rizzuto will take place Monday at the same Montreal church where services were held for his grandson early this year.

The funeral will begin at 11 a.m. ET Monday at the Church of the Madonna della Difesa (Notre-Dame-de-la-Défense), in the heart of the city's Little Italy.

The church was the scene of the funeral for Rizzuto's 42-year-old grandson, Nick Jr., who was murdered execution-style last Dec. 28 on a residential street in Montreal's Notre-Dame-de-Grâce district.

Once again, Vito Rizzuto — Nicolo's son and Nick Jr.'s father — will likely not be allowed to attend the service, as he remains in a Colorado prison, serving a 10-year sentence for racketeering related to a triple murder.

A spokesman for the U.S. Federal Bureau of Prisons said Friday there is a process that would allow Rizzuto to ask to attend a family funeral, but such requests are "very rarely" granted. "If an inmate's security level is such that they would require armed guard, and I can't speak to this case, then it would normally not be granted based on security," bureau spokesman Edmond Ross said from Washington, D.C.

Visitations were set for Saturday evening and Sunday afternoon and evening at the Loreto Funeral Complex, owned by members of the Rizzuto family.

Shooting remains a mystery

As friends, family and associates prepared to say their farewell, police investigators were still trying to piece together what happened Wednesday evening when Rizzuto, 86, was killed at his home in the Cartierville district of the city.

'We advised them a few times and they seemed to be fed up.... They said, 'We know about that. Don't come back.''— Commander Denis Mainville, Montreal police

Officers combed the dense woods behind Rizzuto's mansion where police believe a gunman hid before firing the fatal shot through a window.

Investigators are asking the Rizzuto family for access to surveillance cameras perched around the home as they search for clues.

Montreal police Commander Denis Mainville said investigators had notified the Rizzuto family that they were hearing rumours of threats against senior members of the family.

"We advised them a few times and they seemed to be fed up. They told us they were fed up to see police officers knock at their doors and advise them," said Mainville. "They said, 'We know about that. Don't come back.'"

Theories circulate

Experts on the underworld say the fact a reputed Mafia kingpin was killed in his home is unusual.

Retired RCMP organized crime analyst Pierre de Champlain said when members of the Mafia want to kill a leader, it's usually done in public.

De Champlain said such killings are rarely done at the target's home and even more rarely with family members present.

Author Antonio Nicaso speculated the killing was an attempt to isolate Vito Rizzuto. Nicaso said someone may be trying to "burn the ground" around the younger Rizzuto so there is nothing left when he is released from prison.

With files from The Canadian Press