U.S. baffled by Russian jet "bombing"

Among the theories U.S. officials are considering is that the bomb may have been placed near a fuel line on the doomed Airbus jet, and that it was just large enough to ignite a fire using the fuel in the aircraft’s tanks, two sources familiar with internal discussions told The Daily Beast.

If that was the case, it’s possible that investigators might not find tell-tale explosive residue that would prove a bomb had been detonated, the sources said, requesting anonymity in order to discuss sensitive information related to the ongoing investigation of the crash.

But others see evidence of a more traditional attack.

A former senior U.S. official who was shown an investigation photograph of the wreckage told The Daily Beast that a portion of the underside of the plane shows small, quarter-sized holes and looked like something had blown out of the plane from the inside.

This information led the former official to conclude that the jet was brought down by improvised explosive device, possibly packed with nails and other shrapnel to blow as big a hole in the side of the plane as possible. From there, the plane could have broken up in mid-air, which is about the only thing U.S. officials are sure happened, since the wreckage is spread over a vast area.