A reward for information leading to a conviction over the suspicious 1993 death of 17-year-old Allison Newstead in the NSW Hunter Valley has been increased to $750,000.
The teenager was last seen by her parents on Wednesday, October 6, as she left their home at Cessnock to go to a local cafe.
They reported her missing the following day when she failed to return.
Ms Newstead's body was recovered by police a week later at an abandoned colliery in Pelton, about 8km away.
An investigation to determine the circumstances surrounding her death led to a coroner's inquest in 1994, which was terminated and referred to the Director of Public Prosecutions.
A 30-year-old man was charged with concealing Ms Newstead's body and perverting the course of justice but was acquitted in 1997.
Since then, the case has been pursued by strike force detectives from the Unsolved Homicide Unit.
Ms Newstead's mother Loretta said life for her family changed forever 29 years ago.
"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," Mrs Newstead said on Saturday.
"We really need somebody to be held accountable for the heartache, grief and anguish we ... have had to endure."
Homicide Squad Commander Danny Doherty said it was hoped the boosted reward, originally set at $100,000, would encourage someone holding on to information to come forward.
"Allison's naked body was found underneath sheets of corrugated iron and physical evidence at the scene suggests she was likely dragged to that location," Detective Superintendent Doherty said.
"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."
Police Minister Paul Toole said it was critical anyone with information provides it.
"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," he said.
