Eva Plunkett retired last December and the Conservative government subsequently scrapped her watchdog role, saying it would save money and eliminate duplication.
She had a staff of eight and a budget of about $1 million.
The government says the Security Intelligence Review Committee — a panel of federal appointees — will take over the inspector general's functions.
In her first public comments on the matter, Plunkett said it is "ridiculous" to think the review committee, known as SIRC, could do the same job of probing the Canadian Security Intelligence Service that her office did.
"They don't do the same kind of work at all," she said in an interview. "They don't go into the same depth, the same detail. And they're basically part-time people."
The two watchdogs were different bodies with distinct roles, Plunkett said — the same message she delivered to federal officials last fall when they first approached her with the idea of merging the two organizations.
As inspector general, Plunkett, 60, served as the public safety minister's eyes and ears on the intelligence service — a sort of early warning system to point out brewing problems.
The review committee, as the name suggests, carries out studies of CSIS activities and looks into complaints, issuing public findings in an annual report.
"SIRC is a public forum for people to complain. It's also a forum to make the public aware of problems," Plunkett said.
"The IG's office was, get in there and identify the problems and point them out to the minister and say, 'You have to fix this before it becomes an issue for the public.'
"There's no minister that's going to be able to know everything about everything. And I can guarantee you that no director (of CSIS) will point out the flaws."
Plunkett, who's enjoying retirement in the countryside with her horses, says she's not bitter about her office's demise. "I feel bad for Canada. And I feel kind of bad for the minister, because I think it was poor advice to suggest to him that this wasn't worth having."
She noted that SIRC, while served by an executive director and staff, is composed of appointees who work part-time and meet in Ottawa only periodically.
She suggested that's no substitute for taking on the task full-time, as she did, meeting with CSIS officials regularly at the agency's headquarters.
"It takes you at least a year in the job to learn the right questions to even ask the service," Plunkett said.
"(The SIRC members are) all very qualified, intelligent people in their own field, but it does to take a while to understand the environment."
Plunkett denies there was duplication in the work of the two watchdogs.
"We co-ordinated. We gave SIRC every year a copy of our work plan," she said. "So they knew exactly what we were doing. Because there were so limited resources in either shop, it would be just stupid not to share."
The inspector general's key function was to produce an annual certificate stating whether CSIS had strayed outside the law, contravened ministerial direction or exercised its powers unreasonably.
In her final certificate, Plunkett found CSIS continued to flout policy and made a serious number of reporting errors. She warned that CSIS's reputation and effectiveness would suffer if the problems weren't addressed.
The review committee will receive the equivalent of two extra staff positions to help it assume the job of preparing the annual certificate, said SIRC spokesman Adam Green. One is likely to be a former member of Plunkett's staff.
Green defended the quality and depth of the review committee's work, suggesting it was comparable in style if not content to that of the inspector general. "From what I've seen, SIRC already does a lot of what the IG was doing."
Plunkett doubts SIRC will fill the void left by her office.
"If they staffed up with the proper kind of people and they had the will and a full-time chair, possibly they could do it, sure," she said. "But not the way they currently function."
Plunkett acknowledged most Canadians had little or no idea what her office did, but said those who understood the role "should feel a huge loss and should be concerned."
She said she takes pride in having served as inspector general — and makes no apologies for being something of a thorn in the side of CSIS director Dick Fadden.
"I'm sure Dick Fadden went home and thanked the Lord that I was gone."
She predicted that some day, there will be a scandal that ignites a call for more scrutiny of CSIS.
"The people who work at the service are all really hardworking, dedicated people," Plunkett said.
"But they're people, and people make mistakes."
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