John Ronald Brown, 49, appeared in the ACT Supreme Court on Friday, when his angry supporters threatened and attempted to intimidate members of the media.

One threatened to shoot this reporter and another grabbed a news camera lens. Some others shoved a different journalist and tried to stop him entering the court building.

Brown was due to be sentenced, having previously pleaded guilty to a charge of maintaining a sexual relationship with a child in late 2019 and early 2020.

Agreed facts show Brown preyed on the son of some long-term friends, initially discussing the boy's sexual experiences.

He then exposed himself to the child in the driveway of the boy's north Canberra home one night, encouraging the victim to perform a sex act on him.

There was then an incident during a party at the child's home, where Brown molested the boy in his sister's bedroom.

When Brown subsequently went on an international cruise with the child's family, he fondled the boy in a bed on the ship.

The abuse only ceased when the boy's father caught Brown exposing himself to the child in a cruise ship cabin.

Brown, who was reported to police upon the ship's return to Australia, pleaded guilty in August last year.

His sentencing, which was initially listed for October 2021, was adjourned until Friday for a few reasons, including to allow time for his lawyers to obtain medical material.

Justice Michael Elkaim on Friday said psychologist Douglas Boer had produced a "very significant" report, which posed a problem.

The judge quoted a section of the document that indicated Dr Boer believed Brown was not guilty by reason of mental impairment, namely major depressive disorder and alcohol use disorder.

Justice Elkaim described such an opinion as "entirely inconsistent" with Brown's guilty plea.

"It just seems to me that this is not right," he said.

Brown's barrister, John Purnell SC, told the court a mental impairment defence was not available to his client because the 49-year-old had voluntarily consumed excessive quantities of alcohol.

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Mr Purnell said he only wished to rely on Dr Boer's opinion to argue Brown's intoxication was a mitigating feature of the man's offending.

But Justice Elkaim said he was "distinctly uncomfortable" with this because "either Mr Brown had a mental impairment at the time of offending, or he didn't".

He ultimately adjourned the matter at the request of Crown prosecutor Trent Hickey, who said it would be inappropriate to proceed if Justice Elkaim may yet reject Brown's guilty plea.

As he granted the adjournment, Justice Elkaim apologised to the families of both Brown and the 49-year-old's victim.

"You are all entitled to expect that justice will be done swiftly and without delay," the judge told those in court.

"I apologise to the families that there's going to be a delay, but there just has to be."

The judge reiterated previous comments that a sentence of full-time imprisonment for Brown was "almost automatic", saying any lesser penalty would need to be based on proper medical evidence.

He said the court would benefit from receiving an expert opinion from someone other than Dr Boer, hence the adjournment.

Justice Elkaim ultimately listed the sentence hearing to recommence on May 25.

Brown will remain on bail in the interim.

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