The RCMP used cellphone-tracking technology in a way that was "not lawful" six times, Canada's privacy commissioner said in a report released Thursday.

Mobile device identifiers (MDI) — also referred to as IMSI catchers — work by mimicking a cellphone tower to interact with nearby phones and read the unique ID associated with the phone's International Mobile Subscriber Identity, or IMSI. That number can then be used to track the phone, and sometimes to intercept text messages or calls.

Between 2011 and 2016 the RCMP used IMSI catchers in 125 criminal investigations, 29 of which were in support of other Canadian law enforcement agencies, the report from Daniel Therrien's office found.

In the majority of cases, the RCMP obtained a warrant to use their IMSI catchers. In 13 cases, no warrant was obtained. Seven of those were what the RCMP call "exigent circumstances" — cases requiring the police to act quickly in order to "prevent the loss of life or grievous bodily harm."

The remaining six cases took place during a time when the RCMP was operating under the notion that no warrant was required — between March and June 2015.

The force made the decision to stop obtaining warrants to use the device after receiving guidance from the National Wiretap Expert Committee (NWEC), which provides legal advice to law enforcement and prosecutors.

In June 2015, the RCMP once again began requiring its officers to obtain a warrant before using the device. ​

Therrien's office launched an investigation into the RCMP's use of IMSI catchers in early 2016, after receiving a complaint from OpenMedia, a group that advocates for a surveillance-free internet.

The group wanted to know whether the RCMP was using the devices to collect tracking data, monitor large groups of people and intercept voice and text communications. It also wanted clarity around whether a warrant was required to use IMSI catchers, and under what circumstances.

More transparency

Up until last spring, the RCMP was cagey about admitting its use of IMSI catchers. In April, a months-long CBC News/Radio-Canada investigation revealed that someone was using IMSI catchers in the area around Parliament Hill. At the time, Public Safety Minister Ralph Goodale said Canadian agencies were not involved and that the RCMP and CSIS were investigating. That investigation is ongoing.

Laura Tribe, executive director of OpenMedia, applauds the privacy commissioner's report, which comes after her group filed a complaint in March 2016 about the RCMP's use of IMSI catchers. (CBC )

After the CBC News/Radio-Canada report, the RCMP held a technical briefing for a select group of reporters about IMSI catchers and how the force uses them.

Therrien said in his report that he is now satisfied the force is in compliance with all of Canada's laws when using mobile device identifiers.

The report said the devices the RCMP uses "are not capable of intercepting private communications" like calls or text messages. The report also said any third-party information collected by the RCMP is being properly secured and destroyed at the end of any court proceedings.

Therrien did praise the RCMP for the access it granted his office during his investigation, but warned the RCMP to "continue to make efforts toward openness and accountability in terms of the technologies it employs in its law enforcement activities."

OpenMedia's executive director is happy with Therrien's report and said the force must continue to heed the privacy commissioner's call for transparency.

"To make sure that when the RCMP is using these devices and implementing new policies that they're really clear and forthcoming with the public from the start — as opposed to having to go through these really long investigative processes to get this information out," Laura Tribe said.

In a statement, RCMP acting deputy commissioner for specialized policing services Joe Oliver said, "The RCMP is committed to finding ways to strike a balance between public transparency on the use of the technology and, at the same time, protecting this important tool for public safety and law enforcement purposes."

How IMSI catchers are used

The report also offers a glimpse into how the RCMP use the IMSI catchers. The force has 10 devices, and first used one in 2005.

The RCMP will set the device up in at least three different locations to collect data. After gathering the IMSI numbers in the areas, the data is filtered to see which numbers were found in the same locations as the suspect or suspects. In order to connect an IMSI number with a suspect, another warrant is required ordering a telecom provider to give authorities the name, address and phone number connected to the IMSI number.

The RCMP use the technology in a variety of investigations including those relating to national security, organized crime and during kidnappings.