MONTREAL -- Quebec's corruption inquiry has heard its fair share of explosive allegations. The latest one is about an actual explosion.

A witness Thursday described the frightening methods used to keep an asphalt cartel in place, including the one time his car was blown up when he ran afoul of his fellow schemers.

Gilles Theberge was a director at Sintra, a construction company that was one of four partners in a cartel that controlled the supply of asphalt around Montreal.

He said they conspired to jack up the price 30 per cent higher than what would have been charged under a free-market system.

He said he quit his company after some dramatic events on June 15, 2000.

Theberge was jolted at 2:45 a.m. by a loud, crackling noise -- which he quickly learned was the sound of his car blowing up.

With a charred wreck in his driveway, he made some phone calls.

His first call was not, however, to the police. He said he first called his boss to quit, and to inform him that this collusion scheme had officially gone too far.

He said he also called construction magnate Tony Accurso, another member of the alleged four-company asphalt cartel. Accurso, the longtime head of a sprawling construction empire, has come up repeatedly at the inquiry.

He was allegedly also involved in a sewage cartel, according to key witness Lino Zambito, and allegedly had a corrupting influence on politicians, with paid vacations and trips on his yacht. Previous inquiry testimony has alleged that he has Mafia ties.

Theberge said he called his powerful ally to ask if he knew anything about the car bomb. He says Accurso told him he'd heard nothing about it.

The previous day, Theberge and a number of other construction types had gathered at Accurso's new restaurant in Laval. He says one of the other men, Joseph Borsellino, had asked him if he planned to compete for a $4 million contract in the municipality of St-Laurent.

Theberge recalled replying that it was neither the time, nor the place, to discuss such things. Borsellino made it clear, he says, that Sintra should bow out of the bid.

The men agreed to pick up the discussion at a later point. They never got the chance, because Theberge quit his job immediately after the explosion.

Theberge shared other anecdotes about how intimidation was used to keep the corrupt system in place.

One time, he said, a Mafia-linked man nicknamed "Mr. Sidewalk," Nicolo Milioto, came to tell him that the broken windows at his next-door neighbour's house were a warning.

He said Milioto told him the intention was to break the windows at Theberge's own house -- "but the guy got the wrong house."

He says he sometimes received late-night phone calls, with no one on the other end of the line, when a bid was due. He also says another construction boss told him about a bomb placed under his car, too.

Theberge says he concluded that it was generally easier to say yes to his competitors, and recuse himself from a bid, in order to keep the peace.