Police served the interim intervention order on Cheryl's eldest brother Ricki Nash preventing him from stalking, approaching or contacting the Victorian man, who cannot be named.

The protected person was due to face trial in the NSW Supreme Court this week over the death of the three-year-old toddler at Fairy Meadow Beach in 1970.

However he walked free once his 1971 confession to the crime was ruled inadmissible.

The Director of Public Prosecutions chose not to appeal the decision.

The state's Attorney General Mark Speakman asked for independent legal advice on whether the case should return to court but ultimately decided against intervening.

In a Victorian magistrate's court on May 17, the order was made prohibiting Mr Nash from attempting to locate the "protected person", follow him or keep him under surveillance.

Mr Nash cannot communicate with the man "by any means", approach or be within five metres of him, or 200m of his home or workplace.

And he cannot "get another person to do anything he can't do under the order".

The police action was sparked by a text message Mr Nash sent to a third person while waiting for advice from the Attorney General.

It read: "If the AG does not do the right thing I will have do (sic) correct a wrong. I hope my family understand a murderer cannot be allowed to walk free any longer."

Mr Nash, 56, who lives in Victoria, said he was bitterly disappointed about the court action against him and would be contesting the order at a hearing set down for October.

He agreed he had "written and said things in anger".

"Wouldn't you be angry, wouldn't you say the wrong thing if it was someone you knew, your brother, sister, daughter who was murdered?" Mr Nash told the Mercury.

Mr Speakman earlier told Mr Nash and his brothers Paul and Stephen that appealing the judgment would be cruel and only give them false hope.

"I have told members of Cheryl's family that I have concluded that any appeal against the Supreme Court's decision will fail and that I will not be bringing any appeal," he said earlier this month.

"I am sorry for the further distress this will bring to Cheryl's family, who seek justice for her. I am sorry that today I am unable to help end that search."

Mr Speakman was presented with a document outlining why the Grimmers felt the case could be revisited.

But Mr Speakman said he had considered the submissions, applying his own legal training, and sought advice from the Crown Advocate and DPP and was confident any appeal would fail.

Cheryl disappeared from Fairy Meadow beach in January 12, 1970. It is believed that she was strangled to death around an hour after her abduction. The accused was 17 when he confessed to Cheryl's murder. Police did not consider they had enough evidence to charge him, until detectives began re-investigating in 2016. He was charged in 2017.

Laws now require an adult to be present for child confessions to be admissible, but this was not the case at the time. Judge Robert Allan Hulme found that the new laws applied retrospectively.

Mr Speakman said he "wished the circumstances of the interview in 1970 were different" but said he could not bring an appeal that was "doomed to fail".