A former co-worker testified that Cooper had been “addicted to listening to Radio Peking” and often expressed communist views.

ASIO’s regional director said Cooper had a history as a communist sympathiser.

Despite strong objections, Justice Mann permitted the Crown prosecutor to question Cooper about his political and religious beliefs.

Ten local men were called to testify that Cooper had made the most fantastic suggestions to small lunchtime gatherings, exhorting them to tie up police officers, grab rifles, steal beer and rum, “expel all the white people” and seek help from “the Russians and the Chinese”.

In his evidence, Cooper said his words had been taken out of context.

He had opposed violence and instead advocated the formation of mass organisations, including trade unions and political parties, to convince the government that they were ready for self-government.

The judge conceded that the words attributed to Cooper were highly improbable.

“I cannot believe that the accused really expected to see an immediate armed uprising of natives in the Madang area.”

Yet, the judge concluded that this only made Cooper’s utterances all the more sinister, because his real purpose had been to encourage a political movement.

“[H]is intention was to start a movement which would be likely to extend along the Northern coast of New Guinea, and which would cause the utmost embarrassment to the Administration at a time when international attention was critically focused on the situation of primitive people in this and other areas.”

When Cooper appealed, the Australian High Court ruled that much of the evidence was not only “obviously irrelevant and clearly inadmissible”; it should never have been tendered or entertained. Its only purpose was to “create prejudice in the mind of the tribunal”.

Nevertheless, the five judges reached the perverse conclusion that Chief Justice Mann’s consideration of the wrongly admitted evidence had worked “curiously” in Cooper’s favour because Mann supposedly imposed a “remarkably light penalty” of four months’ imprisonment.

The show trial was able to proceed because both the Labor Party, of which Cooper was a member, and the Communist Party, refused to assist or defend the young man.

After his release from jail, he campaigned for self-government for Papua and New Guinea, speaking at public meetings and writing for various magazines, but remained politically isolated.

In April 1965 he tragically committed suicide.

The High Court’s dismissal of Cooper’s appeal was the third such decision in just over a decade.

In 1948 and 1949, the court upheld the Chifley Labor government’s jailing of two leaders of the Communist Party, Gilbert Burns and Lance Sharkey, who made statements refusing to support Australia militarily in response to hypothetical questions about a war against the Soviet Union.

The High Court ruled that the prosecution need not prove that the accused subjectively intended to “excite disaffection”.

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Dr Michael Head is Associate Professor of Law at the University of Western Sydney