The guy is running for the cockpit with a backpack, yelling. Bad sign.
Actually the guy was running to get off the plane. From ccn.com:
Dave Adams, a spokesman for the Federal Air Marshal Service, said Alpizar had run up and down the plane's aisle yelling, "I have a bomb in my bag." Adams said Alpizar then fled the aircraft and marshals confronted him on the boarding bridge.
http://www.cnn.com/2005/US/12/08/airplane.gunshot/index.html