KUALA LUMPUR, Malaysia (AP) — A Malaysian government official says investigators are increasingly sure that a missing jet turned back across the country after its last radio contact with air traffic controllers. And they're becoming convinced that someone with aviation skills was responsible for the change in course.

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The official said only a skilled person could navigate the plane the way it was flown after its last confirmed location over the South China Sea.

In Washington, meanwhile, a U.S. official said investigators are examining the possibility of "human intervention" in the plane's disappearance, adding that it may have been 'an act of piracy." The official also said it was possible the plane may have landed somewhere.

According to the official, other theories are being examined -- but that the key evidence of human intervention is that contact with the Boeing 777's transponder stopped about a dozen minutes before a messaging system quit.

It is appearing increasingly likely that the plane didn't experience a catastrophic incident over the South China Sea, which was initially seen as the most likely scenario. Some experts believe it's possible that one of the pilots, or someone with flying experience, hijacked the plane for some later purpose or committed suicide by plunging the aircraft into the sea.