whatever ignited the fuel of the tank was inside the tank. it didn't come from outside. >> the cockpit voice recorder recovered one week after the crash may provide evidence. the pilot is heard observing a strange reading on a fuel flow gauge. >> that's probably an indication of some type of short circuit going on. this airplane was old, it was getting ready to be taken out of service. >> and there are more clues. one second before the cockpit voice recording ends, there are two dropouts in background noise suggesting a possible arc on the cockpit wiring. investigators believe in this moment high voltage enter the center wing fuel tank igniting the warm fuel vapors. >> that ignition caused overpressurization of the tank that blew out the forward panel of the tank. you can see the indentation where it's very clear on slam down, there's a very clear mark. >> from that position we had fractures that went down into