The chief prosecutor in the explosive Quebec corruption inquiry announced Tuesday he’s quitting because of a perceived conflict of interest.

In a letter to the Charbonneau Commission, Sylvain Lussier said the conflict allegations are unfounded, but he felt his departure is necessary to preserve the integrity of the probe.

It was reported in August that, as part of his private legal practice, Lussier once represented an asphalt company cited in inquiry documents.

The company, Asphalte Desjardins, was raided Tuesday morning by the province’s anti-corruption squad, along with two other firms, CTV Montreal’s Stephane Giroux confirmed.

"As you know, some doubts have been raised about me in regards to a possible appearance of a conflict of interest due to an old file unrelated to the mandate of the commission," Lussier wrote in his letter to the commission, dated Monday.

"After careful consideration, even if these doubts are unfounded, factual or legal, it seems to me that the public interest will be better served if I remove myself as chief prosecutor ... so as to avoid any possibility that my participation may put in question, in any way, the integrity of this work."

Lussier will be replaced by a senior commission lawyer, Claude Chartrand, on an interim basis.

Lussier’s surprise departure came as one of the key figures in the corruption probe announced he is leaving the construction business.

Construction mogul Tony Accurso, who faces several charges, including corruption and tax fraud, has denied allegations of his involvement with the Mafia that surfaced during testimony at the Charbonneau Commission.

But in a letter to his employees, Accurso said that his departure from the construction empire he built is the best thing for the business.

"After much thought, beginning more than a year ago, I have decided to retire completely from the business world,” he wrote.

"After more than thirty years at the head of these enterprises I believe it is best to leave them to people who are younger and more energetic and able to surmount the challenges they face in the future."

Accurso ran a network of construction companies that were involved in major public-contract projects in Quebec. His firms have also been involved in federal projects.

After provincial and federal investigators raided Accurso’s offices as part of a larger crackdown, he and several other men were charged fraud, conspiracy and corruption.

Corruption inquiry continues

Meanwhile, a City of Montreal lawyer grilled the Charbonneau Commission’s star witness, Lino Zambito, on the stand Tuesday.

Zambito was challenged to provide concrete evidence to back up his allegations of widespread corruption in municipal and provincial politics.

Zambito, a former construction boss, has testified that he had to pay a three per cent kickback from contracts to Montreal mayor’s political party.

But when pressed for details Tuesday, Zambito said he could not remember who specifically told him to fork over the cash.

With files from The Canadian Press