The chief prosecutor for Quebec's public inquiry into construction-industry corruption has resigned.

Sylvain Lussier said "doubts have been raised about a possible appearance of conflict of interest" related to an old case he worked on as a lawyer. Lussier said the concerns have "no basis in fact or in law," but out of a sense of caution for the integrity of the Charbonneau commission, he is quitting.

Earlier Tuesday, a company Lussier once represented, Asphalte Desjardins, was raided by Quebec's anti-corruption squad as part of its investigation into possible collusion in the awarding of public construction contracts.

Lussier represented Asphalte Desjardins in 2007 and 2008 in a court battle between rival siblings of the Desjardins family, which owns the company. He doesn't mention the company by name in his resignation letter.

The ties between Lussier and Asphalte Desjardins were first brought to light in August, but he would not comment about it at the time. A witness at the Charbonneau commission had named that company in June as part of a group of firms that over-charged the Quebec government for public-work contracts.

A report last year in Montreal's La Presse newspaper also pointed out that Lussier was representing the City of Montreal in a lawsuit brought against it by its auditor general. The city's contracting process has been under intense scrutiny during the Charbonneau commission, forcing Lussier to withdraw as Montreal's counsel on the auditor's lawsuit.

'Extraordinary jurist'

The commission said in a news release that it accepted Lussier's resignation "with regret" but recognized that it was in the best interests of the public inquiry. "His departure deprives [the commission] of the services of an extraordinary jurist," the statement said. 

The Montreal lawyer and partner at the firm of Osler, Hoskin and Harcourt previously represented the Canadian government at the Gomery commission, which inquired into the federal sponsorship scandal.

During the summer Quebec election campaign, he tangled briefly with the Coalition Avenir Québec party's star candidate, anti-corruption whistleblower Jacques Duchesneau, who had testified at the Charbonneau commission but was unhappy with the questions he was asked.

The Charbonneau commission has named one of Lussier's assistant prosecutors, Claude Chartrand, as a temporary replacement.

Read Lussier's resignation letter below.

With files from The Canadian Press