'End of the road' in toddler's cold case

For nearly 50 years, the family of murdered toddler Cheryl Grimmer has been searching for justice.

But they were delivered a "kick in the guts" on Friday, as the NSW attorney-general ruled out appealing a key judgement in the cold case.

A man was due to face trial in May over the three-year-old's disappearance but the Supreme Court in February ruled a 1971 police interview - during which the then 17-year-old confessed to murdering the little girl - inadmissable.

Justice Robert Allan Hulme's decision was based on the fact there was no parent, adult or legal practitioner present at any stage of the interview.

The Director of Public Prosecutions decided not to appeal and subsequently withdrew the murder charge due to a lack of other evidence.

Cheryl's brothers were outraged by the move, prompting Attorney-General Mark Speakman to seek independent legal advice.

But based on that advice, he concluded that any appeal would fail.

"I know this decision is a kick in the guts for the Grimmer family but I can't bring an appeal which is doomed to fail," Mr Speakman told reporters in Sydney.

"I can't think of any other path for the Grimmer family."

Cheryl vanished from outside a shower block while with her mother and three older brothers at Fairy Meadow Beach in Wollongong on January 12 in 1970.

The former accused - who cannot be named as he was 15 at the time of her death and 17 when interviewed by police - was arrested in Victoria in March 2017 and pleaded not guilty in September 2018 to murdering the three-year-old.

Mr Speakman said there had been a glimmer of hope for the Grimmer family when charges were laid but apologised for not being able to help bring a perpetrator to justice.

"For almost half a century the Grimmer family has lived with an unresolved murder," he said.

"I wish I could re-write history, I wish the circumstances at the interview in 1971 were different.

"Unless there is fresh and compelling evidence, this is probably the end of the road for any prosecution for (the man)."

The attorney-general spoke with Cheryl's three brothers on Friday morning and said they were devastated by the decision after living in hope the crime would be solved and a perpetrator would be brought to justice.

Mr Speakman said he was confident he had left no stone unturned in the case.