André Roy, an in-house investigator for Canadian Tire, was scanning images from the store’s live security cameras last November when a customer in the automotive aisle caught his eye. He says the man, dressed head to toe in black, looked left and right before removing some packaging and shoving an item inside his trench coat.

For half an hour, Mr. Roy watched the short, stocky customer moving from one department to another, discarding packaging and pocketing merchandise. As the man headed toward the cash register to pay for a flashlight, Mr. Roy and his assistant manager moved in.

The suspect, according to Mr. Roy, put up a fight, and it took four employees to subdue him until police arrived. To Mr. Roy’s amazement, a thick wad of $100 bills totaling more than $3,000 fell from the shoplifter’s pocket during the scuffle. He also noticed the man’s Rolex watch and diamond ring. “I was asking myself why someone with so much money would be committing such a petty theft and reacting so violently,” Mr. Roy testified in Quebec Court last week.

The mystery would only deepen following that Nov. 13 arrest.

Court documents and testimony show that the alleged shoplifter was not the unilingual Italian-speaker named Vincenzo Sestito he pretended to be. A fingerprint check after his arraignment revealed he was Nicola Cortese, a cousin and former business partner of an alleged Toronto Mafia boss. Mr. Cortese, who is considered by police to be a trusted soldier in the Calabrian mob, had vanished in 2008 as police in Ontario searched for him on drug, theft and fraud charges.

Among the items he is alleged to have grabbed from the Canadian Tire were a handgun holster, an ammunition pouch for 12-gauge shotgun shells, a black balaclava and a rubber car part that a police source said could double as a silencer. His true identity and his alleged shopping list have led Montreal investigators to question whether his presence in the city last fall could be connected to the sniper attack that killed the patriarch of the Sicilian Mafia, Nicolo Rizzuto, two days before Mr. Cortese’s arrest.

“Concerns were raised about his presence here, but there is nothing particular that we know about,” a source close to the investigation said. A second police source said Mr. Cortese has been asked about the Rizzuto homicide.

“It is certainly of great interest to me that someone like that is in Montreal at that time,” the source said.

One motive police are investigating for the attacks on the Rizzuto family is a power struggle between Toronto’s Calabrian mobsters and the Sicilian Mafia in Montreal.

On Feb. 9, at the conclusion of a two-day preliminary hearing, Judge Pierre Labelle ordered Mr. Cortese, 47, to stand trial on three charges of theft with violence related to the incident at Canadian Tire. He has chosen a trial before a judge alone, and a date has not been set.

Mr. Cortese is also facing eight charges in Montreal alleging fraudulent use of a credit card and a debit card and possession of a forged Italian passport and a fake Ontario driver’s licence. The charges allege that his first use of the stolen credit card in Montreal was on Oct. 25. It was used there again on Nov. 1. Additional charges filed at the Montreal courthouse allege that he obstructed a police officer by providing a false identity and breached a court order related to outstanding charges in Ontario. After pleading not guilty to all charges, he waived his right to a bail hearing and will remain in custody until trial.