In doing so, the judge said in written reasons, the agency put Canadians abroad at potential risk.
The situation arose five years ago when Canadian Security Intelligence Service asked Federal Court for special warrants related to two Canadian citizens — already under investigation as a potential threat to national security — that would apply while they were abroad.
CSIS assured Judge Richard Mosley the intercepts would be carried out from inside Canada, and controlled by Canadian government personnel, court records show.
Mosley granted the warrants in January 2009 based on what CSIS and Canada's top secret eavesdropping agency — the Communication Security Establishment of Canada or CSEC — had told him.
However, Canadian officials then asked for intercept help from foreign intelligence allies without telling the court.
Mosley was unimpressed, saying the courts had never approved the foreign involvement.
"It is clear that the exercise of the court's warrant issuing has been used as protective cover for activities that it has not authorized," Mosley wrote in redacted reasons.
"The failure to disclose that information was the result of a deliberate decision to keep the court in the dark about the scope and extent of the foreign collection efforts that would flow from the court's issuance of a warrant."
Under current legislation, Federal Court has no authority to issue warrants that involve intercepts of Canadians carried out abroad by Canada's "Five Eyes" intelligence partners, Mosley noted.
He said CSIS, which was granted several similar warrants on fresh or renewed applications in relation to other targets, knew the law but deliberately sought to get around the limitation by misinterpreting it.
"CSIS and CSEC officials are relying on that interpretation at their peril and... incurring the risk that targets may be detained or otherwise harmed as a result of the use of the intercepted communications by the foreign agencies," Mosley wrote.
"(The law) does not authorize the service and CSEC to incur that risk or shield them from liability."
The documents show alarm bells went off after the commissioner of CSEC, Robert Decary, tabled his annual report in August.
In the report, he suggested CSIS provide Federal Court with "certain additional evidence about the nature and extent" of his agency's help to the intelligence service.
Mosley ordered both agencies to explain what Decary meant. He did not like what he heard about the hidden foreign involvement in the intercepts.
"This was a breach of the duty of candour owed by the service and their legal advisers to the court," he said.
"It has led to misstatements in the public record about the scope of the authority granted the service."
Mosley made it clear the warrants do not authorize any foreign service to intercept communications of any Canadian on behalf of CSIS or CSEC.
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