Sensitive Department of Homeland Security documents laying out a response to a simulated biological attack on the Super Bowl and marked “For Official Use Only” were left in the seat pocket of a commercial airplane, according to a report on Monday.

A CNN employee found the draft “after action” papers in December along with a travel schedule and a boarding pass for a person who manages the DHS BioWatch program.

Recipients of the reports were ordered to keep them under lock and key after business hours and to shred them before they were discarded, CNN reported.

They were also told not to share the report’s contents with anyone without “an operational need-to-know.”

The cable network said it withheld publication of the document find until after Super Bowl LII because government officials warned that publishing the story earlier could have jeopardized security for Sunday’s night game in Minneapolis.

“This exercise was a resounding success and was not conducted in response to any specific, credible threat of a bioterrorism attack,” DHS spokesperson Tyler Q. Houlton told CNN.

DHS is also looking into how the documents were left on the plane.

CNN said it couldn’t verify the identity of the name on the boarding pass.

The reports critiqued the response by health and law enforcement officials and emergency management personnel to an intentional anthrax release at the Super Bowl during two exercises conducted in July and November.

Juliette Kayyem, a former DHS official, told CNN that misplacing the documents was “a really stupid thing.”

“Who knows who else could have picked this up,” she said.​ ​”The biggest consequence of this mistake​ ​may have less to do with terrorists knowing our vulnerabilities and more to do with confidence in the Department of Homeland Security. In the end, confidence in the federal government at a time of crisis is what the American public deserves.”