Department of Homeland Security (DHS) documents detailing a simulated biological warfare attack in preparation for the Super Bowl were left in the seat pocket of a commercial aircraft, CNN reported Monday.

An employee for the news network reportedly found the documents, which included the phrases "important for national security” and “For Official Use Only.”

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Included with the documents were a travel schedule and boarding pass for an individual who manages the DHS BioWatch program, according to CNN, which noted it was not able to confirm who left the documents on the plane.

The report included recommendations for improvement based on two simulation exercises meant to assess the authorities’ ability to respond to a potential biowarfare attack.

"This exercise was a resounding success and was not conducted in response to any specific, credible threat of a bioterrorism attack," DHS spokesperson Tyler Houlton said in a statement to CNN.

The documents' discovery is being reviewed, with DHS adding that the agency “does not comment on personnel matters or potential pending personnel action."

CNN held off publishing its report until after the Super Bowl Sunday evening, citing government fears that doing so before the annual game could risk security.