My dad's an ex-pilot and he believes it was somehow human error, not a like a bomb or anything, but the pilots not paying attention or something. He expects that something will turn up within the next few hours (like 10 pm PST)....it just turned morning... it would have been difficult to find pieces if either thing had happend.
i read than can tell if the plane blew up in the air or if it went down for other reasons depending on how the pieces scattered on the ocean.
He also said an investigation will probably show similiaries between the Air France Flight 447 crash a few years ago:
http://www.cnn.com/2012/07/04/world/europe/air-france-flight-447-explainer/