Since 2016, the Commonwealth Criminal Code has had a scheme for the continuing detention of "terrorist offenders", where a court is satisfied that a person poses an unacceptable risk of committing a serious terrorism offence if released into the community at the end of their sentence.

The Independent National Security Legislation Monitor is examining through a public hearing in Canberra whether the power is proportionate to the national security threat, meets Australia's human rights obligations and provides adequate procedural fairness and safeguards.

Sydney Institute of Criminology director Andrew Dyer on Wednesday called for an abolition of the scheme due to the restrictions already provided for through an "extended supervision order"- which allows for proportionate surveillance of a released offender - and the "doubtful quality of risk prediction".

"We find it very difficult to imagine circumstances where the state could prove an extended supervision order does not remove the risk posed by the offender to a tolerable extent," Dr Dyer told the inquiry.

Any further detention should only be used as a last resort and in light of strong evidence about the prospect of a future offence, the Australian Human Rights Commission argues.

"Ensuring that laws in this area protect our national security, but also show a strong respect for human rights and freedoms, isn't a sign of weakness in a counter-terrorism response," commissioner Lorraine Finlay said.

"It's a clear indication of the strength of our democracy and our values as a nation."

She said restricting the liberty of offenders who had already served their sentence should be subject to periodic reviews.

The commissioner also raised concerns about the "reliability of the tools that are currently used to predict the risk of future terrorist activity".

INSLM head Grant Donaldson says the use of experts is inherently controversial.

"It's controversial simply because what is required is for relevant experts to assist the court by assessing the risk of a defendant committing an offence in the future," he said.

"That's an unusual and difficult thing and it is inevitably problematic."

The commission's deputy general counsel says offenders should not be detained following their sentence if the risk of reoffending is slim.

Graeme Edgerton argued courts in NSW and Victoria had interpreted the current test as fulfilled if there is a slim possibility of offending but it still provides unacceptable risk "if the potential consequences are very grave".

"We say it should not only 'unacceptable', but also 'probable'," he said.

"In terms of probability, we don't say that should be more likely than not. But there should be some element in there that means that very unlikely occurrences aren't the basis for holding someone in detention as well."

Dr Dyer went further, suggesting the onus should be on the state to prove a future offence is more probable than not if the continuing detention order is to continue.

"We say the state should have to prove beyond reasonable doubt that an unacceptable risk of a terrorist act or the support or facilitation of a terrorist act must exist," he said.

Rehabilitation should also become the focus of the extended detention, Dr Dyer added.

Two continuing detention orders have been made before the supreme courts of NSW and Victoria but no extended supervision orders have been directed by them to date.

The hearing continues on Thursday.

Australian Associated Press