Earlier in the day, U.S. officials told NBC News that “all we know is something quick and catastrophic” happened to the plane.

The investigation will probably take some time, partly because authorities would have to find wreckage and perform forensics test. A full day after the plane disappeared, there were no signs of the aircraft, although the Vietnamese air force spotted two oil slicks consistent with jet fuel off the coast of Vietnam.

In the crash of TWA Flight 800, in 1996, it took more than a year to rule out terrorism.