UK police forces have long shrouded their use of IMSI catchers in extreme secrecy. In October, a report in the Bristol Cable uncovered new evidence that several forces had bought such technology, which UK police refer to as "covert communications data capture," or CCDC.
But, that doesn't mean police forces are going to break with tradition: some agencies have tried to remove evidence of their spending on IMSI catchers from the web, even though the publication of some of these documents is supposed to provide more transparency into the police and how it uses public funds.
"Their insistence on secrecy is in stark contrast to shallow political promises around accountability. There is no question that these devices raise serious data protection issues for the thousands of innocent people who have their personal data collected by these mass surveillance systems," Richard Tynan, a technologist from activist group Privacy International, told Motherboard in an email.
Tynan added that UK police force's stance on IMSI catchers "reveals their contempt for transparency."
IMSI catchers work by pretending to be cell phone towers, and forcing phones in their proximity to connect. The devices then learn each SIM card's international mobile subscriber identity, or IMSI. Some models of IMSI catcher are also capable of intercepting text messages and calls.
One document that showed UK forces' use of these tools was the minutes of a meeting involving Warwickshire and West Mercia police, discussing the upgrade of CCDC equipment.
"Within the West Midlands region both West Midlands and Staffordshire Police have recently purchased and operated 4G compatible CCDC equipment," the document reads.
When asked for clarification, Sarah-Jane Lynch, an Engagement Officer with the West Mercia Police and Crime Commissioner, pointed to a version of the minutes available on the Commissioner's website. Those minutes, however, have redacted the section on CCDC.
Another PDF file was the Metropolitan Police Service's (MPS) "Contracts valued over £2500 awarded between October to December (Q3) 2015-16." That document showed that the MPS had paid over £1 million for "CCDC" services to a company called CellXion.
CellXion sells IMSI catchers and other surveillance equipment, according to company brochures. The company was also granted an export license for some of its products, Motherboard found via the Freedom of Information Act.
There appears to be a gap on the MPS' website where the expenditure document should have been, and the original link for the PDF file returns a "Page Not Found" error.
Samantha Charles-D'Cruz, an information officer from the MPS, told Motherboard in an email that the document "was published on the MPS website in April but had to be removed from the website earlier this month. This was due to the document requiring a redaction for reasons impacting on operational capabilities. Once the redaction has been made the document will return to the website."
Regardless, the original, unredacted documents, which do show that the use of IMSI catchers in the UK is more widespread than previously known, have been mirrored in several places on the internet, including here.