The law enforcement official, who declined to be identified because the investigation is ongoing, said authorities will require significant time to definitively confirm their suspicions that North Korea sponsored the attack, which severely damaged the movie studio's network.
The likelihood of the hackers being brought to justice in the United States is presently regarded as low, said the official.
A threat against theaters planning to show Sony Corp's controversial movie about the assassination of the leader of North Korea was published on the Internet on Tuesday. It promised a "bitter fate" for those who went to see the movie, "The Interview," a comedy whose villain is North Korean leader Kim Jong Un. The movie is scheduled for general release on December 25.
U.S. security authorities said on Tuesday they were investigating the threat but had so far seen no real sign of an active plot. A second U.S. official said on Wednesday that investigators are not aware of any people or entities capable of actually carrying out such threats against cinemas or audiences.
U.S. State Department spokeswoman Jen Psaki said the United States took all reported physical threats seriously, including those against movie theaters, but added:
"At this time we have no specific credible threat information that lends credence to these reports."
North Korea complained to the United Nations in June, accusing the United States of sponsoring terrorism and committing an act of war by allowing the movie's production.
Carmike Cinemas, operator of 278 theaters in 41 states, informed Sony late on Tuesday that it would not show the film, a person familiar with the matter told Reuters. Sony has also canceled the New York premier, which had been planned for Thursday.
© Thomson Reuters 2014