Police seeking public assistance again to help solve murder of Penny Hill, who was murdered near Coolah 28 years ago

NSW Police Force is seeking the public's assistance again to help solve the murder of Penny Hill, which occurred in the state's Upper Hunter nearly three decades ago.

The then 20-year-old was found unconscious with severe head and facial injuries on Cassilis Road, near Coolah, about 8am on Monday, July 8, 1991.

She was taken to John Hunter Hospital, where she died two weeks later, on Sunday, July 21.

In 1992, a coronial inquest in Mudgee returned an opening finding on the cause and manner of death.

Detectives from the State Crime Command's Homicide Squad began further investigations into Ms Hill's murder under Strike Force Samdon, before a second coronial inquest was held in 2012.

That also delivered an opening finding and was returned to investigators, who pursued a number of new lines of inquiry.

However, no one has ever been charged in relation to her death.

Her mother, Jeanette Hill, said the past 28 years has caused unbearable pain.

"There is simply no way to describe the immense agony of losing a child," she explained.

"Every day I am reminded of Penny, of the tragic way in which she was taken from us, and of the life she never got to live.

"It has been almost three decades that we have been searching for answers and once again we ask that anyone in the community who might know what happened to our daughter, please come forward and help police.

"Our family, and our Penny, need peace."

In July, the NSW Government increased the reward for information, which led to the arrest and conviction of those responsible for her murder, to $1 million.

Homicide Squad Commander Detective Acting Superintendent Mark Henney said the Hill family deserved closure.

"Penny had only just moved to Coolah - to begin her first job as a nanny at the Black Stump Motel - just three days before her body was found," he added.

"Detectives have made a number of public appeals to the community for any information that could help investigators solve this horrific murder.

"Over the years, a number of leads have been pursued.

"And, we are committed to getting justice for Penny and providing answers for her family."

Anyone who can help is urged to contact Crime Stoppers on 1800 333 000 or https://nsw.crimestoppers.com.au

Information is treated in strict confidence.

The public's reminded not to report crime via the social media pages.