Federal prison authorities are under criminal investigation for possible illegal surveillance, The Globe and Mail has learned. The probe centres on Correctional Service Canada's use of a dragnet surveillance device inside a penitentiary.

Fallout from the 2015 surveillance incident, involving a device that CSC officials called a "cellular grabber," has led to a lawsuit from jail guards and a criminal inquiry by the Ontario Provincial Police.

Under the Criminal Code, indiscriminate surveillance campaigns can be deemed crimes that merit prison sentences. Federal security officials do not get blanket exemptions, even if they themselves work to manage prisons.

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The case at hand started with a desire to locate prisoners' contraband cellphones, but ended up with a warden apologizing to his own staff for inadvertently spying on them.

The make and model of the device in question are being withheld from the public, which generally is familiar with such machines by names such as "Stingrays," "cell-site simulators" or "IMSI catchers."

"IMSI catchers are not localized. It would get anything that's in range and won't discriminate," explained Tamir Israel, a lawyer at the Canadian Internet Policy and Public Interest Clinic.

On Monday, The Globe and Mail reported on the RCMP's courtroom bid to keep its use of a similar device secret.

In the winter of 2015, officials at Warkworth Institution, a medium-security prison in Ontario, grew alarmed by prisoner drug overdoses. On Jan. 20, one CSC official sent an internal e-mail, according to federal court documents related to the civil suit, saying "there are phones all over the institution and this is how they are organizing the introduction of contraband."

Officials in Ottawa, records show, put out a request for an outsider who could perform "surveys of radio traffic" to "confirm the presence of cellular phones inside institutions." The winning contractor, according to federal court documents, was a Quebec-based engineer named Peter Steeves, who said he could do the job for $7,500 in fees, plus $2,000 in travel expenses.

Contacted Monday by The Globe and Mail, Mr. Steeves said he is no expert in the legalities of interception. "I'm just a guy trying to make a living – I really don't know the law," he said. Asked about the police probe, he said, "I know I have to go for an interview. I have been told it's a criminal investigation."

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Access to information records show that last April, a device was shipped to CSC from Florida. Details are mostly being withheld, but it weighed 38 kilograms and its manufacturer was a Britain-based surveillance-machinery firm, Smith Myers.

The "pilot program" at the Warkworth Institution started rolling out in the late spring. By August, CSC officials arranged an internal meeting to review the "cellular grabber to better understand its capacity," according to an e-mail now filed in court. Officials wanted to know "how to force" a phone to communicate its specific location, or how to list phones on a map of the prison.

Before long, CSC officials began asking for even more specifics – such as how to figure out whether phones were sending texts or calls. On Sept. 3, one official asked for the "total activities of cellular devices from inmates, staff …"

Prison guards learned of the program, and pushed back. "How does this device bend a radio signal … to eliminate the inclusion of staff areas?" one guard asked in an e-mail to his bosses.

By the end of September, Warkworth's warden, Scott Thompson, sent an apologetic e-mail to all staff, according to access to information records. "Unfortunately, I knew that by trying to intercept what the inmates were doing, I would also be provided information about cellular devices being used in non-inmate areas," his e-mail said. The warden relayed that the device "provides make, phone numbers and sim-card numbers" and, also, "recorded all voice and text conversations."

With that, he assured his jail guards that any of their inadvertently captured communications wouldn't be used against them. "I am sorry if this information causes stress to any of you," he said.

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Some CSC e-mails contradict the warden, stating explicitly that the device did not capture any conversations beyond three text messages intercepted in a bid used to showcase its capabilities. (On Monday, the contractor, Mr. Steeves, told The Globe that the device "does not capture voice at all.")

At the end of October, the Union of Canadian Correctional Officers took their bosses to court. In a lawsuit, they complained their their privacy rights had been violated – and that CSC had spied upon them.

"Look – we're all about getting the contraband out. We're in. If there's technology to do that, we're there," explained Jason Godin, a union vice-president in an interview. "But, God damn it," he said, "… you can't spy on private conversations of staff members."

Mr. Israel suggests that the correctional officials who acquired the device were likely operating in a legal vacuum.

"Because no agency to my mind has openly acknowledged to using these in court, no court has provided guidance as to what the [legal] authorities should be," he said. Some federal officials, he added, "may be under the impression they can just deploy these IMSI catchers without any authorization at all."

CSC officials have recently stopped giving statements to lawyers pursuing the civil suit. According to Federal Court filings, that's because they have become worried to have learned there is now also a criminal probe.

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"The Ontario Provincial Police is currently conducting a criminal investigation into the monitoring of cellphones at Warkworth Institution," reads a motion filed earlier this month. Because OPP detectives are now interviewing CSC officials, the latter "have significant concerns about providing affidavits while an investigation is under way."

Spokespersons for the OPP and CSC won't comment on the specifics of the investigation.

Correctional officials originally defended their use of the device by saying they had "authority to monitor and intercept communications to ensure the security of institutions." But they have stopped saying this now that they face civil and criminal investigations for alleged unlawful surveillance of jail guards.

Court filed e-mails show that, in the end, CSC seized only three contraband cellphones smuggled into Warkworth.

With a report from Laura Stone in Ottawa