The United States knew North Korea was behind the Sony Pictures hack because it had secretly infiltrated the country's computer networks in 2010, according to the New York Times and Der Spiegel.
The newspapers cited US officials and leaked documents from the National Security Agency.
The New York Times said hidden software had alerted US intelligence services to North Korean hacking activity.
The United States was quick to point the finger at North Korea for the devastating hack on Sony pictures late last year, and imposed sanctions.
North Korea has continued to deny any role, and some independent cyber security experts have also expressed doubts.
Now leaked documents and testimony from former officials have found their way into the public domain, and appeared to back up Washingon's case, the BBC reported.
The New York Times said US spy agencies had drilled into the Chinese networks that connect North Korea to the outside world, and set up what amounted to an early warning system for any attack.