On Tuesday, FBI Director James Comey told the Senate Intelligence Committee that encryption found on smartphones is “overwhelmingly affecting” law enforcement investigations and operations, reports Reuters . Interestingly, Comey revealed that the FBI has still been unable to access the data on one of the San Bernardino attackers’ phones because of its encryption.

“In San Bernardino, a very important investigation for us, we still have one of those killer’s phones that we have not been able to open,” Comey said at the hearing. “It’s been over two months now. We’re still working on it.”

Comey did not reveal the make or model of the smartphone, but both the iPhone, as of iOS 8, and many Android devices now enable encryption by default. It’s a feature that has been a contentious issue between technology companies and governments and their security agencies around the world. After the Snowden revelations about the NSA’s Prism program, many private sector tech companies took a renewed look at encryption to keep their users’ data safe. But that encryption is something law enforcement agencies say hurts their ability to investigate and uncover criminal and terrorist acts and plans.

Speaking to a Senate Judiciary Committee in December, Comey said, ”There’s no doubt that the use of encryption is part of terrorist tradecraft now because they understand the problems we have getting court orders to be effective when they’re using these mobile messaging apps that are end-to-end encrypted. We see them talking about it all over the world—it is a feature, especially, of ISIL’s tradecraft.”

On Tuesday Comey again reiterated that smartphone encryption hurt security agency’s abilities to fight terrorism, but he said that though the technology affects national security work, when it comes to encryption “overwhelmingly this is a problem that local law enforcement sees,” noting that it hinders investigations into murder, car accidents, drug trafficking, and child pornography, reports Reuters.

But many tech companies and privacy advocates counter that Comey’s statements about encryption hindering law enforcement investigations are exaggerated. The Berkman Center for Internet and Society at Harvard released a study last month in which it concluded that despite encryption technologies it is getting easier for intelligence agencies to gather information about people.

“As data collection volume and methods proliferate, the number of human and technical weaknesses within the system will increase to the point that it will overwhelmingly likely be a net positive for the intelligence community,” the authors of the study wrote. “Consider all those IoT devices with their sensors and poorly updated firmware. We’re hardly going dark when–fittingly, given the metaphor–our light bulbs have motion detectors and an open port. The label is ‘going dark’ only because the security state is losing something that it fleetingly had access to, not because it is all of a sudden lacking in vectors for useful information.”