The tortured remains of George Brown, a Sydney horse trainer, were found inside his incinerated car at the top of Bulli Pass about 11pm on April 2, 1984.

A Wollongong coroner later found the 38-year-old had probably been force-fed a large quantity of alcohol by his killers.

There were multiple fractures to his legs and his arm was bent backwards. Something had connected hard with his head, causing a network of cracks to spread across his skull like a spider's web.

There were other fractures above his right ear - one a saw-like crack and another just above it, nearly 6.5cm long. The fire had burnt away his lower legs and his forearms.

His watch had dropped from his burnt wrist and stopped ticking at 10.56pm.

The NSW government has announced a $1 million reward for information that leads to the conviction of those responsible for his murder.

Homicide Squad Commander, Detective Superintendent Scott Cook, said detectives would welcome any information from the community that may help provide answers to Mr Brown's family.

"We know George Brown worked at the horse stables at Rosebery throughout the day and evening where he was last seen 35 years ago, but he did not arrive at his Kensington home as planned," Det Supt Cook said.

"A significant aspect of the investigation is around one of Mr Brown's horses who performed poorly at a race meet in Doomben, Brisbane, two days before his death.

"We would like to hear from anyone with information about possible race-fixing at that meet or anyone who knew of any fears or concerns George held from any person or group just prior to his murder.

"Investigators are also interested in the movements of Mr Brown's vehicle, a 1973 green Ford Falcon sedan with NSW registration 'GMH 498', so if anyone remembers seeing that car, we would like to speak to you," Det Supt Cook said.

Mr Brown's sister, Jean O'Leary, said the family have never given up hope of finding out what happened 35 years ago.

"I had a very close relationship with my brother, George, and helped raise him after our mother died," Mrs O'Leary said.

"George was a good man and his death has impacted our entire family.

"Every year since he was murdered, I have hoped that someone would come forward because it's the right thing to do.

"This year, now there is a $1 million reward on the table, I am pleading with anyone who knows something to contact the police," Mrs O'Leary said.

The reward can be provided to anyone who has information that leads to the arrest and conviction of the person or people responsible for Mr Brown's death.

Anyone with information that may assist Strike Force Comboyne investigators is urged to contact Crime Stoppers: 1800 333 000