The decision quashing his conviction for providing material support to terrorism was an anticlimax, since it had long been accepted his guilty plea could not stand. He had admitted to a crime that did not exist.

A conviction of another Guantanamo Bay detainee had already been overturned on this basis. A US court held that the acts of that person could not be turned into a crime after the event.

This reflects one of the most important aspects of any democratic legal system — that a person is entitled to act in accordance with the law as it stands. The law must not be applied retrospectively.

The same argument applied in Hicks’ case. He has said he received training from al-Qaeda and met Osama bin Laden before being captured in Afghanistan in late 2001.

In doing so, he committed no offence, because the crime of providing material support to terrorism was added to the US statute book years later.

The US government recognised this, and so put no submissions to the US military court suggesting Hicks’ conviction should stand.

Its only argument was a technicality — that Hicks could not have his conviction overturned because he had waived his right to appeal.

This last-ditch defence failed because, even though Hicks said in his pre-trial agreement that he would waive his appeal rights, he had not submitted the papers for this within the required 10 days.

As a result, his appeal rights remained, and the military court said “having concluded that the appellant’s case is properly before us for appellate review, both parties agree that the appellant’s conviction cannot stand on the merits”.

The decision is another blow to the already discredited military commissions at Guantanamo Bay.

For Hicks, the decision clears his record. Despite this, many continue to cast him as a terrorist.

In any event, no charges can be laid against him under Australia’s vast body of anti-terrorism laws.

These were introduced in 2002, months after he was taken into US custody.

The response of the Australian government has been underwhelming.

Attorney-General George Brandis merely “notes the decision by the US Court of Military Commission Review into Mr Hicks’ conviction”.

He also said government dealings with Hicks had always been “in accordance with Australian laws”.

This is true, but it illustrates the weaknesses of those laws.

The law does not require the government to look after the interests of Australian citizens abroad.

Hicks said he was tortured at Guantanamo Bay. Recent investigations give credence to his claims.

Australian governments have made no attempt to get to the bottom of his claims. Instead, they have seized the royalties from his book through proceeds of crime legislation.

There is no sign the Abbott government will depart from past approaches. No apology will be offered, nor is compensation likely for injuries suffered at Guantanamo Bay, or for the seven months he spent at Adelaide’s Yatala prison on the basis of a flawed conviction.

It can only be hoped the government will at least recognise there is no further prospect of Hicks being convicted for his past, and allow him to get on with his life.

George Williams is the Anthony Mason professor of law at the University of NSW.