Giuseppe Borsellino was guarded when answering questions about the beating, which he said left him with severe facial injuries that required reconstructive surgery.
"I don't know why [it happened] and it could have been for a number of reasons. It could be linked to construction," he said. "I've tried to forget the incident."
Commission chair France Charbonneau pushed Borsellino further, asking him to give the commission more details on the motive behind the assault, which, he said, he did not report to police.
"If you were beaten to the point that you were disfigured and had to be hospitalized for a reconstruction of your face, you must have some idea why you were beaten like that," she said.
"I have some ideas. Maybe I didn't pay my debts. Maybe I didn't do a job well. It's maybe two or three reasons," Borsellino replied.
The construction boss said he was in his office in July 2009 when three men came in and assaulted him. He said the men didn't say anything at the time to indicate their motive, and he had no warning that they were coming.
"I did not make a complaint, and I went on to my business and went back to work," he said.
Borsellino said it was the only time he has been the victim of physical violence.
Borsellino did say he was acquainted with reputed members of the Montreal Mafia, including Vito Rizzuto and his late father Nicolo Rizzuto.
He explained that his parents came from the same village in southern Sicily, Cattolica Eraclea, as the Rizzutos and that he had been to Montreal's Consenza Social Club, which law enforcement authorities have alleged acted as one of the Rizzuto clan's headquarters.
He said he only was in the club in a social context and in the back room, which was later the subject of intense video surveillance by the RCMP, to use the washroom or make a phone call.
Borsellino stressed that he only knew the family because they were members of the Sicilian community in Montreal and that he had no business dealings with them.
He did however tell the commission that he believes the construction industry has been infiltrated by the Mafia. He stopped short of naming any names and hedged his response, saying that it was all second hand knowledge.
"What I've heard is that there's infiltration. What entrepreneurs have been infiltrated, that I can't say," he told the commission.
He said he tried to keep his head down and focus on his business. Those people that he was dealing with were businessmen and entrepreneurs and not, to his knowledge, members of organized crime groups.
"Did you pay a cut to the Mafia?" Charbonneau asked.
"No. Absolutely not," Borsellino replied.
Borsellino denied ever attending a family event held by the Rizuttos, including Nicolo Rizzuto Sr.'s funeral in 2010.
He said he may have been invited to the wedding of Vito's son Leonardo, but said if that was the case, the invitation would have came from the bride's side, who were family friends.
He couldn't recall if he went to the wedding and blamed memory loss for the beating for his vague responses.
Cash in envelopes
Earlier in the day, Borsellino was questioned further about cash and gifts he'd given to city officials as part of a kickback scheme that had already been the subject of the testimony of several former bureaucrats called to the witness stand.
Borsellino said he handed around $100,000 cash to city engineer Gilles Surprenant as part of a collusion scheme to rig the bidding process between 1995 and the mid-2000s.
After that, Borsellino said his firm made a decision to no longer "do business" with Surprenant.
France Charbonneau suggested that, by that time, the system of contract inflation had already become the norm, and Borsellino no longer needed Surprenant.
Borsellino also admitted that he gave around $115,000 in cash to former City of Montreal engineer Luc Leclerc, who the entrepreneur said was responsible for approving extra work billed to the city.
Leclerc told the commission last fall that he took as much as 25 per cent of the contingency costs on inflated bills or false invoices construction companies charged on public projects.
Borsellino said he paid off Leclerc in about 80 per cent of the projects they both worked on, estimating that amounted to between five and 10 separate payments.