prosecutors reprogrammed the plane's autopilot to crash. he changed the cruising altitude from 38,000 feet to just 100 feet. the cockpit voice recorder indicates the co-pilot locked the captain out. he then ignored screaming and pounding of the cockpit door putting the plane that steady descent and crashing it into a mountain. how was this pilot able to pull off this horrific act? >> reporter: he cannot imagine why a pilot would do this. bugs forscythe knows how. a retired military commercial pilot he says he's flown thousands of ours in the a320 cockpit. >> normal lock and unlock. >> reporter: he's used the switch hundreds of times. >> the unlock you have to pull up and hold it. a light comes on and says the