How do we know about anything, Gary? How do we know about the goings-on in Washington or Ferguson? Not that we believe all of it, depending on the source. Clergymen describe a bounteous hereafter but no one has ever seen it.

Google fragging in Vietnam, go to your library, get a book, check Amazon. The assault by soldiers on their officers in Vietnam is writ large in the public record. No need to look for survivors to confirm it. It's part of history.