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Speaking at the International Conference on Cyber Security at Fordham University today in New York City, Comey revealed for the first time that the FBI saw IP addresses previously used by North Korea.
Comey also cited the similarity of malware used in prior cyber-attacks.
"Some serious folks have suggested that we've got it wrong," he said, noting that there were other sources and methods he could not reveal but were used by the FBI in their investigation.
"There is not much in life I have high confidence about," Comey added, defending the conclusion of federal officials that North Korea was responsible for the attack. "I have very high confidence in that attribution"
Comey's remarks come just days after the United States levied new sanctions on North Korean officials and its defense industry.
Earlier this week, Sony's CEO, Kazuo Hirai, broke his silence at the 2015 International Consumer Electronics Show in Las Vegas, where he began his presentation by addressing the difficult few weeks his company had faced.
"I think it would be remiss if I didn't mention Sony Pictures Entertainment and the comedy movie 'The Interview,'" Hirai said. "Freedom of speech, freedom of expression, freedom of association, those are very important lifelines of Sony ... and our business."