Can anyone tell me how to find out if a Vietnam pilot who trained in the US is KIA or MIA. He married a American while training here, then was never heard from again.

The wife had a child, she has passed away. She thought he had been shot down because the letters stop suddenly.

She wrote the US gov. but because he wasn't American they could not tell her anything.

Any help to point me in the right direction would be appreciated.

The child doesn't want to interfere if the man is
alive, but would like to know what happened to him.