Veteran Wollongong detective Frank Sanvitale reinvestigated the case, had a suspect charged and brought before the court, only to see him walk free in February this year.

The events that have followed the shock breakdown of the prosecution case have led the seasoned Wollongong detective to doubt whether "the powers that be" want the truth to come out.

He has received no explanation from the NSW Department of Public Prosecutions about their decision not to appeal a judge's ruling to reject the key piece of evidence - a signed confession from the suspect made 16 months after three-year-old Cheryl disappeared from Fairy Meadow beach in 1970.

He's had no advice on what would be needed to get the case back before the courts and no satisfactory response from the NSW Cold Case unit as to whether the investigation into Cheryl's death and murder is still active or lying dormant.

Speaking exclusively to the Illawarra Mercury, Det Sanvitale said he can't let the case rest, not for himself nor the victim's family.

"I don't sleep. Cheryl comes to me at night. This little blonde girl in her swimsuit holding out her hand to me. It's the same recurring dream. I can't let this go," Det Sanvitale said.

"I know my investigation was all by the book, all done properly, and yet the suspect has walked away again. For the second time."

Det Sanvitale, who has been reluctant to speak publicly, spent two years reinvestigating Australia's oldest cold case.

He believes that in the initial investigation, vital pieces of evidence were never identified and "no true attempt to find suspects were made".

It took Det Sanvitale and his partner Det Sgt Damian Loone just three hours to find two suspects, including the one charged and later allowed to walk free, who were earlier said to be "too hard to find".

Another sticking point is the fact no one interviewed Cheryl's oldest brother Ricki, who was at the beach when she was abducted.

Ricki Nash, who was eight at the time, still clearly remembers his sister being lifted up to a water bubbler by an unknown male. His version, never reported, matches evidence given about a suspect all those years ago.

Det Sanvitale won't publicly reveal details about the prosecution case or why he was so convinced his investigation would lead to a conviction - holding out hope the case may be re-opened, despite the inadmissibility of the confession.

He wants answers and believes the Grimmer family has gone through enough.

"The most disturbing situation I found was that we identified a suspect but the existing evidence, his confession, was suppressed by a judge because of what we call retrospective law," Det Sanvitale said.

"It's a law which makes people criminally responsible for doing an act that was not actually against the law at the time it was done," Det Sanvitale said.

"But retrospective law can work in reverse. The law can legalise an action even though at the time it was committed was criminal, allowing a murderer to walk free," he said. "I am sure that the spirit of the law was never introduced to allow murderers to walk free."

The Grimmer case was the last murder case for Det Sanvitale who has spent 20 years in the NSW Police Force.

Three quarters of those years were working on high profile cases as a senior detective.

"My last case, the murder of three-year-old Cheryl Grimmer, was also the most disturbing of my career," he said. "After more than two years working on the Grimmer case the stress and self-recrimination was the final straw.

"I knew after we had arrested the accused for the murder of Cheryl Grimmer I could not do the job anymore. I had no support or encouragement from my supervisors, just criticism."

Det Sanvitale recalls sitting at his desk finalising his paperwork for the high profile Splashes nightclub murder in Wollongong when his supervisor threw him a thin folder.

The detective had a reputation for his meticulous and relentless work style.

His boss jokingly said: "Have a look at this, if you cannot solve it no one can" .

Det Sanvitale started to look through the brief file but two weeks later suffered a heart attack.

"I returned back to work three months later, like a dog with a bone I picked up the folder and recommenced the investigation.

"I needed the rest of the brief of evidence which I discovered were in nine boxes at State Archives," he said.

Three months later Detective Sgt Loone jumped on board to assist.

"I recall Sgt Loone and I stood over those boxes of evidence. Thousands of old typed sheets ... I will never forget when Det Sgt Loone said to me 'the person who murdered Cheryl will be somewhere in these boxes'."

"We divided the two boxes up and Damian said come have a look at this. In his box was the confession. I looked at it and said 'how did they miss this'. Then we started going through it word for word."

The rest for now is history but Det Sanvitale, who was medically discharged from the police force earlier this year, can't let it go.

"I have become emotionally involved and remain in contact with the family," he said. "The case is disturbing because the killer is known but the existing evidence is insufficient to support an arrest or conviction."

Det Sanvitale says he is obsessed with the case and continues to assist the Grimmer family.

"Imagine that was your little three-year-old daughter never to see her alive again, no body ever found and no grave site to mourn over, would you be relentless in finding the truth?" he said.

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"It's one of the saddest cases I have worked on. Especially in cases where there is no arrest and particularly those involving children, homicides or sex crimes, investigators become emotionally involved with the victim's families and remain in contact with them for many years. This case is that one for me."

Det Sanvitale is pleading with the Cold Case Unit to keep searching for that vital piece of evidence that will bring the case back before the court.

"It's gone cold. After two years of work now nothing, no explanation to the two investigators. Nothing."

"My tenacity and commitment and patience to deal with frustration and disappointments has gone," he said. "The Grimmer family have been kicked in the guts too many times over the last 50 years.

"I blame myself for being committed to the case and with the help of Detective Loone giving them hope that I had solved the oldest cold case in Australian history.

"In the end I feel comfortable with my investigation and I know we have the right person."

Illawarra Mercury