A retired Melbourne schoolteacher has made astonishing claims about how he was threatened by government thugs over what is regarded as Australia's greatest UFO mystery, before being contacted by federal agents close to the American president.

On April 6, 1966, about 200 Westall High School students, teachers and Clayton South residents witnessed a large silver cigar-shaped 'flying saucer' hover above the school's oval and the nearby Grange Reserve.

The incident has been recounted before, immortalised in UFO-shaped play equipment for kids to climb on at the reserve and even retold in a documentary, but one of the teachers who witnessed the extraordinary events has since revealed new details of what happened next.

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