Questions are being asked about the behaviour of a NSW magistrate who expressed controversial views about crime and sentencing in a call to talkback radio.

Key points: The talk back call included controversial comments about Aboriginal sentencing

The talk back call included controversial comments about Aboriginal sentencing Legal expert says Mr Degnan may face claims of bias as a result of his views

Legal expert says Mr Degnan may face claims of bias as a result of his views Mr Degnan declined to speak to the ABC

The magistrate — who the ABC has confirmed is sitting magistrate David Degnan — failed to identify himself as a judicial officer when he made the call, which included strident comments about Aboriginal crime.

Now a former NSW District Court judge is warning the magistrate is likely to face claims of bias from defendants who appear before him in court.

Mr Degnan made the call to Sydney broadcaster Robbie Buck's Breakfast program on 702 ABC Sydney in February this year and identified himself as "Dave", who "works in the criminal justice system".

The call followed a segment which discussed crime and sentencing, including the Indigenous-specific Circle Sentencing.

Sorry, this audio has expired David Degnan's call into ABC Local radio

"By the time people are sent to jail they are nearly always recidivists," Mr Degnan said in the talkback call on February 17.

"Jail is always a last resort, so this idea that jails don't work, I'm sorry, they do because they lock people up that don't get the message."

During the call, Mr Degnan became animated when he moved the discussion to Aboriginal crime.

"This thing about Aboriginal people in custody, they're committing the offences," he said.

"That's why they're in custody. No-one's trying to target the Aborigines. Each offender comes to the court and they're dealt with individually."

When questioned about whether rehabilitation programs could be more effective than prison, Mr Degnan said programs existed in every local court in NSW — a claim disputed by other judges who say such services are often not available in remote jurisdictions.

"Some people just keep offending," Mr Degnan said.

"Most of the people that do offend, they've been given bonds, they've been sent to different programs, they've had supervision, but they don't seem to get the message. And then eventually, yes, they'll end up in jail."

Magistrate denied he made call

Some lawyers and magistrates across NSW recognised the caller at the time of the call, and fellow magistrates questioned Mr Degnan directly.

Mr Degnan is understood to have initially denied to at least two magistrates he was the caller.

The ABC questioned Mr Degnan and chief magistrate Graeme Henson about the call at the time, and both magistrates said they had no comment.

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But recently at a Sydney dinner, Mr Degnan admitted in front of fellow lawyers and magistrates to making the call. He said at the dinner the controversy had "all blown over".

Mr Degnan is regarded as a tough sentencer by some lawyers.

Comments could have ramifications for future cases

Retired District Court judge John Nicholson SC said Mr Degnan may now face bias applications from defendants.

"I'd be surprised if there hasn't already been applications made to him to recuse himself on the basis of views he's expressed," Mr Nicholson said.

"There may be some Aboriginal people who would be uncomfortable coming before a judicial officer who had expressed opinions in respect of Aborigines are therefore committing offences.

"He will have lost the opportunity to make an impact on the community in terms of balanced judicial decision making. I'm not suggesting he's not doing that, but the problem is the people coming to his court may fear he won't do that in their case."

Monash University Law Professor Matthew Groves, one of the nation's leading experts on judicial fairness and bias, said the Guide to Judicial Conduct strongly cautions against judges speaking to the media.

"Talkback radio and the like as especially dangerous for judges," Professor Groves said.

"It is not that these things are not good for debate. The problem is that they are not the natural terrain of judges."

Both Mr Degnan and chief magistrate Graeme Henson offered no comment on the issue today when approached by the ABC.