FBI Director James Comey said on Tuesday that federal investigators have still been unable to access the phone contents belonging to one of the San Bernardino killers due to encrypted technology.
Comey told the Senate Intelligence Committee that the phenomenon of communications "going dark" due to more sophisticated technology and wider use of encryption is "overwhelmingly affecting" law enforcement operations, including investigations into murder, car accidents, drug trafficking and the proliferation of child pornography.
Comey cited the San Bernardino attack as an example. Syed Rizwan Farook, 28, launched an Islamic State-inspired attack with his wife, Tashfeen Malik, 29, in the California town in December that left 14 people dead.
Comey and other federal officials have long warned that powerful encryption poses a challenge for law enforcement and national security professionals.
Technology experts and privacy advocates counter that so-called "back door" access provided to authorities would expose data to malicious actors and undermine the overall security of the Internet.