A conditional indemnity offered by the Director of Public Prosecutions could be key to solving German backpacker Nancy Grunwaldt's disappearance, a retired detective says.
A case that has rocked the Tasmanian community for almost three decades, Ms Grunwaldt was last seen riding a bicycle about four-kilometres south of Scamander on March 12, 1993.
The 26-year-old travel agent had traveled from New Zealand to Tasmania, via Melbourne.
A coronial inquest released more than a decade after the backpacker vanished found Ms Grunwaldt died as a result of foul play.
The disappearance has been linked to Victoria Cafasso's murder, but decorated former Detective Sergeant Bob Coad said it was totally wrong to connect the two cases.
"There's not one piece of evidence that ever come to fruition or come to the fore to link the two," Mr Coad said.
The retired cop had a 35-year career with Tasmania Police, spending majority of that time investigating major crimes in the state.
"Just because you're retired it doesn't take away your knowledge or efforts to see something through," Mr Coad said.
Ms Grunwaldt's body was never found, but Mr Coad believes she was likely hit by a motorist and those responsible dumped her body.
A missing person report wasn't filed until six weeks after the last sighting of Ms Grunwaldt, putting police on the back foot from day one.
Mr Coad continues to follow the case religiously, keeping notes and newspaper clippings from the investigation.
There were pieces of evidence that Mr Coad said never eventuated into much, but he was confident it was relevant to the case.
Between Ms Grunwaldt disappearing but before a missing person report had been made, Mr Coad said someone left a message a solicitor in Hobart's phone.
"It was a male caller, terribly upset and distraught. He was pleading and wanted urgent help because he'd been involved in a terrible accident on the East Coast," Mr Coad said.
"He pleaded over and over that he needed to talk to somebody and wanted advice. My thoughts are, come the next day there's nothing in the papers about accidents or missing persons, so the person scooted back to the mainland."
Mr Coad said it wasn't on the case file, but Hobart detectives went to see the solicitor a few months later.
"It makes sense if this terrible accident happened on the Friday night it connects with the phone call being made on the Saturday morning," he said.
"I know in my heart and gut that some person or persons will come forward if an indemnity is offered."
Mr Coad said conditional indemnities had been used in the past and if Ms Grunwaldt's death was a terrible accident, it might encourage someone to come forward and explain the circumstances.
"What there needs to be is a conditional indemnity to the person involved and any witnesses there too," he said.
"I have pushed for that application to be made for a number of years."
A Tasmania Police spokeswoman said an indemnity was only offered by the Director of Public Prosecutions as a last resort.
"Blanket indemnities are not offered in cases where it is possible a person died as a result of a criminal act," the spokeswoman said.
"As with all missing persons cases in Tasmania, families deserve answers to what happened to their loved ones and police investigations always remain open."
According to the DPP guidelines, the criminal justice system should operate without the need to grant any concessions to persons who participated in alleged offences in order to secure their evidence in the prosecution of others.
"However, it has long been recognised that in some cases this course may be appropriate in the interests of justice," the guidelines said.
A reward of up to $30,000 for information that leads to the successful prosecution of an offender still stands.
Anyone with information is asked to call police on 131 444 or Crime Stoppers on 1800 333 000.