Retired detective Bob Coad on a breakthrough in the Nancy Grunwaldt case

Now three decades on, the infamous cold case is heating up as decorated former detective Bob Coad makes an explosive revelation.

Even in retirement, Mr Coad has remained invested in solving the case, advocating for the persons involved to come forward to provide closure for Ms Grunwaldt's family.

"Fairly recently, I spoke to a woman who contacted me and said her son had come to her telling her he was struggling with getting on with his life," he said.

"He then asked his mother if she remembered the female tourist who went missing in Tasmania in 1993, saying that he knew what happened to her.

"The woman explained that her son had said he had been a passenger with another man and they had been driving south along the back roads from George Town to Hobart.

"They were under the influence of drugs while driving when they had come around a corner and hit Nancy.

"They panicked. Nobody was about, so they put her body and all her property in the car and continued travelling south.

They then buried Nancy, her bike, and her belongings in a shallow grave in bushland."

Mr Coad said this series of events lined up perfectly with corroborations by two male callers, one who called and left a message on a solicitor in Hobart's phone.

"There was a message left by a very upset male caller, who he described as sounding absolutely distraught," he said.

"The caller said he wanted help and advice and had to speak to someone.

"He said he'd been involved in a terrible accident on the East Coast and had hit a cyclist.

"He kept repeating that it was a terrible accident and wanted help."

Mr Coad said the man made the call sometime between late Friday, March 12, 1993, and early Saturday, March 13, 1993.

"The solicitor had gone into his office that Saturday morning and found the message," he said.

"After listening to it, he'd combed the papers for serious crashes that weekend, but when none were reported.

"The man didn't call back [and] he didn't pursue it any further.

"By the time he relayed this information to detectives following the report of Nancy's disappearance nine weeks later, the tape was already recorded over many times."

Following the nationwide airing of the television show Australia's Most Wanted in 1997, which featured an episode on the disappearance of Nancy Grunwaldt and the murder of Victoria Cafasso, a second phone call was made by a distraught male caller.

"The operator described him as extremely emotional," Mr Coad said.

"He called the Brisbane CrimeStoppers explaining that he had trouble living with the fact that he had hit and killed a girl riding her bike on the East Coast of Tasmania and didn't know what to do now.

"To me, both of the calls and the story related to me by the mother run hand in hand."

Tasmania Police confirmed they are still actively investigating Nancy's disappearance, saying just last week, bushland was searched in relation to the case.

"We are unable to comment or confirm the specific location searched," Inspector Craig Fox said.

"Confirming information has the potential to jeopardise the investigation or the potential to identify any informants.

"Information that Nancy has been struck by a car, with multiple people in the car, and has been transported to another location and buried has been investigated by Tasmania Police."

A reward of up to $500,000 for information that leads to the successful prosecution of an offender still stands.

Anyone with information is asked to call the police on 131 444 or Crime Stoppers on 1800 333 000.