Mohamed Harkat was released on bail in 2006 after being held for 3½ years without trial under a national security certificate. (Fred Chartrand/Canadian Press)

Canada's spy agency did not tell a Federal Court judge that a key informant in the terrorism case against Algerian refugee Mohamed Harkat failed a lie detector test in 2002, according to a top secret letter released Friday.

Judge Simon Noël, who is conducting a probe into the way Canadian Security Intelligence Service has handled the Harkat case, made the contents of the letter public on Friday.

The letter says the administrator of the 2002 polygraph test determined the informant was "untruthful" in his or her answers to certain "relevant questions." Portions of the letter, which was written by CSIS lawyers, are blacked out as they contain sensitive information. The identity of the informant was not revealed.

Noël chastised the spy agency last week after receiving the letter for witholding information from him. Until now, the nature of that information was unknown.

The federal government insists Harkat is a member of al-Qaeda. Harkat has denied any involvement with terrorism.

The former Ottawa pizza delivery man and gas station attendant was released on bail in 2006 after being held for 3½ years without trial under a national security certificate.

CSIS review

In its letter, CSIS says the lapse was inexcusable and admits the mistake may raise questions about the other security certificate cases.

The certificates had allowed the government to detain and deport non-Canadians who are deemed a threat to national security.

The letter says CSIS is now doing an "exhaustive review" of all material from informants in national security certificate cases.

Noël intends to recall three CSIS witnesses next week as part of his review of the spy agency's conduct in this case.

With files from The Canadian Press