OTTAWA - Closed-door evidence from the Canadian Security Intelligence Service about Mohamed Harkat's alleged involvement with extremists must be viewed very skeptically given the spy agency's faulty track record, says a lawyer for the Ottawa man.

Counsel Matt Webber told the federal judge presiding over the Harkat case Tuesday that CSIS's history of "systematic, unlawful conduct" means evidence presented in secret cannot necessarily be trusted.

"I'm saying, be very, very cautious."

Lawyers for Harkat, a former dishwasher and pizza delivery man, are wrapping up arguments in hearings to determine whether the national security certificate filed against him should stand or be tossed out.

Harkat was arrested in December 2002 on suspicion of being an al-Qaida sleeper agent.

The government wants to deport Harkat to his native Algeria under the certificate -- a rarely used tool in Canada's immigration law for removing suspected terrorists and spies.

Harkat's lawyers have painted him as a hardworking refugee trying to build a new life in Canada with wife Sophie.

Counsel David Tyndale said Monday that Harkat's version of reality is "irreconcilable" with the government's view of him as a member of Osama bin Laden's terror network.

Justice Simon Noel will weigh evidence given in open court and closed sessions before deciding whether the government had reasonable grounds to file the certificate. A decision isn't likely before September.

Harkat, who arrived in Canada in 1995, denies any involvement with terrorism.

Noel hinted Tuesday, as he has previously, that Harkat's testimony contradicts classified arguments the judge has heard in camera -- sessions Harkat and his lawyers are not allowed to attend.

The notion his client might be fibbing prompted Webber to suggest the other side may well be lying, and therefore Noel should cast a wary eye on the federal evidence.

In a ruling last fall, Noel said CSIS "undermined the integrity" of the court's work by failing to disclose relevant details of a polygraph examination of a source in the Harkat affair. CSIS neglected to tell him a secret informant failed portions of the lie-detector test -- a lapse the service itself has called "inexcusable."

Webber pointed to last week's release of a report by the inspector general of CSIS that chastised the spy service for a notable increase in the number of mistakes in its reporting -- errors that could have serious "negative consequences" for those the spy agency investigates.

He argued it would be unfair to condemn Harkat based on sketchy reconstructions of conversations that took place more than a decade ago and on confidential sources whose credentials cannot be tested by defence counsel.

CSIS contends Harkat is not telling the truth about his association with Ahmed Said Khadr, a late Canadian aid worker who had ties with Bin Laden.

Harkat has acknowledged only meeting Khadr in passing in Canada.

Details about the allegations that Harkat worked for Human Concern International, the Ottawa-based charity that employed Khadr -- and carried out tasks on his behalf --have not been revealed in open court.

"If that information is from a human source, reject it," Webber said Tuesday.

The experienced criminal lawyer said he has often seen such confidential sources crumble in the witness box under cross-examination. Yet it appears no such questioning is taking place in the certificate hearing.

"You have not seen the whites of that person's eyes," Webber told Noel.

Noel said immigration law allows a judge to accept any kind of evidence, then assign relevant weight to it.

Webber acknowledged Noel was free to do so, but urged him not to take CSIS's word about circumstantial evidence.

"Keep an open mind."