"The charade that took place at Guantanamo Bay would have done Stalin's show trials proud," Mr Richter said in a commentary for The Sunday Age. "First there was indefinite detention without charge. Then there was the torture, however the Bush lawyers, including his attorney-general, might choose to describe it. Then there was the extorted confession of guilt."

The controversial deal came a day after the US Defence Secretary, Robert Gates, told a congressional committee in Washington that tribunal verdicts would lack credibility because of the reputation of Guantanamo around the world. A law professor at the University of Richmond in the US, Carl Tobias, said the "machinations" in the Hicks trial "suggest the accuracy of Gates's Thursday testimony about global perceptions of the military trials". The Hicks deal stunned even the military prosecutors, who were seeking a much longer sentence. It only emerged later that Colonel Morris Davis, the lead prosecutor, and his team had been kept in the dark about negotiations between the Hicks defence team and Susan Crawford, the Defence Department lawyer who oversees the tribunals.

Colonel Davis said he had learned of the deal at lunchtime on Monday, before Hicks's first appearance. The sentence of nine months shocked him. "I wasn't considering anything that didn't have two digits," he said. Colonel Davis said he could have chosen not to sign the papers but it would have been just a symbolic move.

Maureen Byrnes, the executive director of the New York organisation Human Rights First, said the Hicks proceedings "illustrated everything that's wrong with these military commissions". "The plea deal in particular has the taint of coerced statements and secrecy. The deal effectively censors anything Mr Hicks might allege about what he says he suffered and implausibly characterises the last five years of his detention as justified under the laws of war," she said. Lex Lasry, the Australian QC who observed the tribunal for the Law Council of Australia, said the conditions attached to the deal were suspicious. Hicks would be locked away and forbidden to speak publicly until after the federal election later this year.

"What an amazing coincidence that, with an election in Australia by the end of the year, he gets nine months and he is gagged for 12 months from talking about it," Mr Lasry said. A lawyer with the American Civil Liberties Union, Ben Wizner, said if Hicks was such a menace to Western security, "why was he given a sentence more appropriate for a drunk-driving offence?"