Police and the NSW state government will offer a reward of $750,000 for information into the suspicious death of a 17-year-old girl at Cessnock in 1993.
Allison Newstead was last seen by her parents on Wednesday, October 6, 1993, when she left their Cessnock home, heading to a café.
She was reported as missing the following day after she failed to return.
Her naked body was found by police under sheets of corrugated iron at an abandoned colliery in Pelton, about 8km south-west of Cessnock, seven days later. Police said evidence at the scene suggested the body was dragged there.
"Investigators do believe there are still people out there - particularly associates of Allison from the time - who have not yet spoken to police and may have useful information," Homicide Squad Commander, Detective Superintendent Danny Doherty said at the weekend, "That includes multiple persons who we suspect may have been there when Allison died, or who have direct knowledge of the circumstances of her death."
In 1994, a coronial inquest into the matter was terminated and subsequently referred to the Office of the Director of Public Prosecutions.
A 30-year-old man was then charged with concealing her body and perverting the course of justice but was later acquitted in 1997.
Since that time, inquiries into Ms Newstead's death have been undertaken by detectives from the State Crime Command's Unsolved Homicide Unit under Strike Force Bain.
In 1998, the NSW Government announced a $100,000 reward for information leading to the arrest and conviction of those responsible for Allison's death. On Saturday, the reward was increased seven-fold.
Loretta Newstead, Allison's mother, said her family's life changed forever the day her daighter died.
"Not a single day goes by that we don't think of Allison and wonder if we will ever know what happened to her on the night she was taken from us," Ms Newstead said.
"We really need somebody to be held accountable for the heartache, grief and anguish we as a family have had to endure for the last 29 years.
"I hope this substantial reward will prompt somebody to come forward with new information and deliver justice for Allison," Ms Newstead said.
Deputy Premier and Minister for Police Paul Toole said it was critical that anyone with information provide it to police.
"It might seem like an insignificant piece of information to you, but even the smallest amount of intel could be the missing piece of the puzzle police need to solve the case," Mr Toole said.
"Officers have worked tirelessly on this case, and I sincerely hope this reward can deliver some answers and closure to Allison's loved ones."
Anyone with information has been urged to contact CrimeStoppers on 1800 333 000.
