That suspect was due to face trial in the NSW Supreme Court this month. However he walked free once the detailed 1971 confession to the crime was ruled inadmissible.

"The legal system has given approval to rip him out of his normal life based on evidence put forward after 50 years, they extradite him, incarcerate him for two years, then in 90 minutes say 'no we are not going to proceed any further'," Cheryl's brother Ricki Nash told the Mercury.

"Then since that time, no one - not the police or the government, or lawyers - have kept us up to date. I'm having to chase, chase, chase, to find out any information.

"Their care factor for us, the victim's family, is zero. They build us up over the last two years and give us hope and then rip it out after 90 minutes of deliberation."

The accused was 17 when he confessed to Cheryl's abduction and murder.

Police did not consider they had enough evidence to charge him, until Wollongong detectives began reinvestigating in 2016.

He was arrested and charged in March 2017, making history as one of the oldest Australian cold cases to reach court.

Laws now require a parent, other adult or lawyer to be present for child confessions to be admissible, but this was not the case at the time.

However Judge Robert Allan Hulme found that the new laws applied retrospectively.

NSW Director of Public Prosecutions Lloyd Babb SC declined to appeal against the decision.

NSW Attorney-General Mark Speakman is now considering the case.

The Grimmer family has presented Mr Speakman with a document, seen by the Mercury, outlining arguments about why a confession to Cheryl's murder should be allowed.

In a statement to the Mercury on Monday the Attorney General said: "The Crown Advocate is now reviewing further material provided to my office on Friday by Cheryl's family and will provide me with further advice.

"I expect to discuss the matter with Cheryl's family after I consider that advice."

In handing down his ruling to exclude the confession Judge Hulme said no parent, adult or legal practitioner was present at any stage of the police interview.

He described the interview as "somewhat troubling", noting a caution was only given during the interview when the teenager started confessing.

The judge said that in the 1971 interview the suspect "told the detectives that he intended to have sexual intercourse with her.

"He did not because she started to scream as soon as he took a gag off her; so he then strangled her, she stopped breathing and he thought she was dead.

"He said he then 'panicked and covered her up with bushes and run for it".

At the time, there was no mandatory requirement, legislative or otherwise, or even a guideline by way of police instruction, for an adult support person to be present during the interview.

The judge also heard evidence from two psychiatrists, who agreed the teenager had a very disturbed mental state at the time and was acting out in various ways.

The Grimmer's believe the case has been dropped over a legal technicality. And one they say is misguided.

Their document, containing 17 points, largely focuses on the argument against the law applying retrospectively in these circumstances.

They believe the accused had no legal right to have an adult present and the police had no obligation to ensure that there was one present.

"This right did not exist in 1971 and was conferred by legislation from 1977 onwards," their document states.

Mr Nash is awaiting a response from the Attorney General.

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