A passenger on United Airlines flight 490, traveling from Denver to Dallas, discovered box cutters in the seat pocket in front of her before takeoff. The Transportation Security Administration (TSA) has confirmed the incident. NBC in Colorado has the story:

"The passenger notified the flight attendant, who told the pilots, who called authorities," said United spokesperson Megan Mccarthy. 

Translation: Passenger "Jane Dough" discovered the security threat, not the security agents tasked with locating potential security threats. The plane had arrived in Denver from La Guardia Airport in New York and was delayed for two hours after the security breach.   

9News in Denver asked TSA spokesman Darin Kayser how the box cutters could have gotten through federal security systems. Kayser said, "Things like this do occasionally happen. That's why we have armed pilots and Federal Air Marshals so that if prohibited items do get on board, there are other layers of security."