and marci. what's so remarkable about this investigation is they still have nothing to do go on. no hard facts. no evidence. until they can find that plane. as the search enters a fifth day, the malaysian military is now exploring the possibility that the boeing 777 en route to beijing lost its tracking signal, banked hard left, and soared hundreds of miles -- >> cannot discount any theory. who had the ability to turn off the transponder? i don't know. >> reporter: the plane's possible u-turn is complicated a malaysian search effort criticized as scatter-shot. now dozens of ships to cover tens of thousands of miles of open water. >> because we've doubled instead of narrowed our search scope today, i think that we're grasping at straws and i think there's a real concern we may never find it. >> reporter: authorities say until wreckage is found, all theories remain on the table, including terrorism. though officials say two iranian men traveling on stolen passports were not found in u.s. terror or criminal databases.