Actually if he'd had any sense he would have locked the door, called ATC and said he thought the Captain was in the hands of hijackers and someone dressed as as the Captain was telling him to open the door or else
When the forces of Law & Order stormed the plane and dragged the real Capt off to durance vile (probably tasering/tear gassing/gagging him on the way) the No.2 could saunter off and disappear.......... I'd bet it would take them 4 hours to confirm who the real Capt was - more if they had to contact Addis
