as the months tick by and no pieces of the plane were discovered. some speculated it was possible the plane had landed. but no communications from the people on board or hijack demand made that seem less possible. mechanical failure. a theory that a catastrophic electrical or mechanical failure brought the aircraft down is still being considered. rapid decompression. the plane suddenly loses cabin pressure and the passengers and crew become unconscious. the plane on autopilot flies until it runs out of fuel and crashes. but without more evidence they are all just theories. leaving grieving families in limbo. wondering what happened to those they lost. sara sidner, cnn. >> in limb bo, joining me, inspector david sousi, and cnn