MONTREAL -- Once entrusted with keeping an eye on the country's spy agency, Arthur Porter is now a wanted man.

The former head of the CSIS watchdog agency was among five people named in arrest warrants issued Wednesday by Quebec's anti-corruption squad for allegations of fraud in one of the country's most expensive infrastructure projects.

Prime Minister Stephen Harper's Conservative government now finds itself facing uncomfortable questions over its decision to appoint Porter -- a medical doctor and cancer specialist -- to a board that reviews some of the most sensitive files held by Canada's spy service.

The warrants say the men are wanted on numerous charges -- including fraud, breach of trust and document forgery -- in relation to the $1.3-billion construction of a Montreal mega-hospital.

The others being sought are: former SNC-Lavalin senior executives Pierre Duhaime and Riadh Ben Aissa; former high-ranking hospital executive Yanai Elbaz; and Jeremy Morris, the administrator of a Bahamas-based investment company linked to the fraud allegations.

Porter and Elbaz are suspected of having accepted bribes from some of the others, the warrants say.

Elbaz, once a top McGill University Hospital Centre (MUHC) executive, was arrested Wednesday. He is scheduled to appear in a Quebec court Thursday.

Canadian authorities are now trying to extradite Porter and Morris from the Bahamas. Porter runs a private medical clinic in Nassau, where he is being treated for cancer.

Quebec's provincial police anti-corruption squad has made numerous arrests over the last year in relation to continuing scandals in the construction industry.

All the events in these latest arrest warrants allegedly took place between Oct. 16, 2008, and Aug. 31, 2011. Porter was director general of the MUHC when the alleged fraud occurred.

He was also head of the Security Intelligence Review Committee, or SIRC, which he joined in 2008 before becoming its chairman in 2010.

Interim Liberal Leader Bob Rae, himself once a member of SIRC, told The Canadian Press that Porter would have been privy to highly sensitive information during his tenure on the board.

"All the members of SIRC have top security clearance," he said. "They would routinely receive any and all information from CSIS that is asked for.

"They would be aware of the overall policy direction of CSIS, particularly concerns of CSIS with respect to threats to the security of the country."

Rae questioned the Harper government's decision to appoint Porter to SIRC.

Porter resigned under unclear circumstances in 2011 and left the country. The federal government has since tightened the screening process for nominees to the intelligence committee.

Public Safety Minister Vic Toews fended off questions about Porter's appointment in the House of Commons.

"Arthur Porter submitted his resignation and it was accepted almost two years ago," he said.

"However, the leaders of the NDP and the Liberal party were consulted prior to his appointment and they consented to the appointment. The allegations that Mr. Porter is facing do not have anything to do with his former responsibilities."

Duhaime, the former chief executive officer of engineering powerhouse SNC-Lavalin, had already been charged earlier this month with fraud, conspiracy to commit fraud and issuing false documents.

Duhaime and another former top executive, Ben Aissa, were charged in connection with a contract involving the building of the mega-hospital.

But police said the charges related to the Wednesday arrest warrant are separate from the ones Duhaime and Ben Aissa already face.

Duhaime is due back in court May 23 and is not allowed to leave Canada. Meanwhile, Ben Aissa has been detained in Switzerland since April 2012 and is awaiting trial there on charges related to alleged corruption, fraud and money-laundering in North African countries, including Libya.

In a statement Wednesday, SNC-Lavalin said it had only just learned of the additional charges against Duhaime and Aissa.

"As we have stated repeatedly, SNC-Lavalin has and will continue to co-operate fully with all authorities who request our assistance," the company said.

"We have voluntarily turned over information that we have to local and other authorities for them to take any actions that they may consider appropriate."

The head of the Caisse de depot et placement du Quebec, which manages Quebec's public pension plan, said the allegations against the former SNC-Lavalin executives should not tarnish the entire company.

"We don't have a lot of established companies with global potential in Quebec and Canada so our perspective is to continue investing in SNC-Lavalin because we are convinced that the company is in a position to respond to the challenges which are incredibly important," Caisse CEO Michael Sabia told a news conference.

"We don't think it's the right time for the Caisse to close the file on SNC-Lavalin. We have a company with a lot of potential, an important company for Quebec and Canada, and our goal is to work with the company, the management and board to encourage them to do the necessary things to clean house, which is absolutely necessary, and also to encourage the development of its potential."

Elbaz worked at the McGill University Hospital Centre from 2002 to 2011. He served as director of technical services from 2002 to 2005. He then was director, redevelopment, planning and real estate management until being terminated in October 2011.

His name has come up during Quebec's corruption inquiry, on a list of names of people who met with a controversial construction magnate at an exclusive Montreal club.

McGill University Hospital Centre chair Claudio Bussandri called for the prosecution of anyone involved in criminal acts.

"The alleged actions of Dr. Porter and Mr. Elbaz are clearly contrary to our values and our code of ethics," he said in a statement. "Please rest assured that we will continue to monitor the situation and assess our options, including legal action.

"We wish to reiterate that the authorities have made it clear that no current employee or the institution itself are under investigation."

The arrest warrants "bring clarity to the situation," Bussandri said.

"I speak on behalf of the board of directors and the entire MUHC community in expressing our anger and sadness with the alleged behaviour of Dr. Porter and Mr. Elbaz," he said.

The other person named in the warrants, Morris, is linked to a company called Sierra Asset Management, which police say served as an intermediary between SNC-Lavalin and McGill University Hospital Centre officials.

Both Porter and Morris are listed on the warrants as living in the Bahamas.

Porter has kept a low profile since leaving Montreal in 2011, when questions were raised about his business dealings.

He recently told CBC News he has cancer.

In a rare interview at his health clinic in the Bahamas, Porter said he had done nothing wrong. He characterized the allegations against him as "spurious" and the result of a "witch hunt."

"I mean it just seemed that there were attacks from all angles," Porter told the CBC.

"I mean if you looked at each piece maybe you would say, 'OK, maybe that's an issue, that's an issue.' But it just seemed to be that I was responsible for the snowfall in Montreal."

-- With files from Canadian Press reporters Steve Rennie in Ottawa and Ross Marowits in Montreal