Two prominent witnesses at Quebec's corruption inquiry have quit their jobs. 

The departure of Rosaire Sauriol, vice-president of Dessau, the engineering firm established by his father, comes just days after damaging testimony about his role in bid-rigging schemes for public works' contracts in Longueuil and Montreal.

Robert Marcil, the former head of public works for the City of Montreal, quit his position with SMi Group, an international engineering firm, four weeks after testifying that he knew nothing of bribe-taking by the bureaucrats working under him and denying that he was an integral part of a system of corruption and collusion.

Sauriol leaves job he's held since 1986

"This resignation is effective immediately," the firm Dessau said in a brief news release about Sauriol's departure as vice-president, adding that the firm has worked actively since 2009 "to redress a situation that was unacceptable for the firm and our industry."

As Sauriol himself testified before the Charbonneau commission, Dessau began reviewing all of its business practices and its ethics code that year.

It brought in consultants and made a decision to stop all political financing, he said. In 2010, the firm discussed the files with its lawyers and, the next year, voluntarily disclosed its history of fake invoicing to fiscal authorities.

Sauriol said Dessau had been involved in a false-invoicing practice to free up cash for political-party fundraising for five years.

He testified the company had been part of a cartel of engineering firms involved in bid-rigging that also included SNC-Lavalin, CIMA, Genivar and SM.

"We're guilty, we did it," Sauriol testified.

The commission also heard Dessau employees donated nearly $1 million to the Quebec Liberal Party and the Parti Québécois over a decade — most of which was refunded by Dessau.

Marcil leaves SMi Group 'for personal reasons'

SMi Group released a brief statement about the departure of Robert Marcil from its ranks.

It said all parties had agreed the details of Marcil's departure would remain confidential.

Marcil left his job as head of Montreal's public works department in 2009 under a cloud.

He came under fire at the corruption inquiry for a trip to Italy paid for by construction entrepreneur Guiseppe Borsellino.  He was also confronted with evidence that he personally funnelled insider information to Borsellino, the head of Garnier Construction.

He described that as a "one-off" incident, and he refused to acknowledge he was in a conflict of interest because of his friendships with people in the construction industry even as he sat on selection committees to choose firms for public works contracts.

At one point, an exasperated France Charbonneau, chair of the commission, said Marcil would have to be "an imbecile" or "incompetent" not to recognize that conflict of interest.