British police claim a criminal investigation they are conducting into journalists who have reported on leaked documents from Edward Snowden has to be kept a secret due to a “possibility of increased threat of terrorist activity.”

Following Snowden’s disclosures from the National Security Agency in 2013, London’s Metropolitan Police and a lawyer for the United Kingdom government separately confirmed a criminal probe had been opened into the leaks. One of the Metropolitan Police’s most senior officers publicly acknowledged during a parliamentary hearing that the investigation was focusing on whether reporters at the Guardian had committed criminal offenses for their role in revealing British government mass surveillance operations exposed in Snowden’s documents.

But now, the Metropolitan Police, known as the Met, says everything about the investigation’s existence is a secret and too dangerous to disclose. In response to a Freedom of Information Act request from this reporter, the force has repeatedly refused to release any information about the status of the investigation, how many officers are working on it, or how much taxpayer money has been spent on it. The Met wrote in its response:

to confirm or deny whether we hold any information concerning any current or previous investigations into the alleged actions of Edward Snowden could potentially be misused proving detrimental to national security.