Twenty-three years on, the question of who gunned down the 17-year-old in his parent's service station remains a mystery.

Shock waves were sent through the Inverell township on October 23 1996, when Billy was found critically injured with gunshot wounds.

His mother Patricia, and step-father Phil Page are pleading for answers into who committed the suspected robbery gone wrong.

"Any information, big or small, could be the missing piece of the puzzle," the family stated.

Emergency services were called to the rear of the roadhouse on Warialda Road at about 9pm on October 23.

Billy was rushed to hospital, however, he died three days later on Saturday, October 26, 1996.

A post mortem examination found he died from two gunshot wounds to the chest and stomach.

"Local police, assisted by the Homicide Squad, commenced an investigation into the circumstances surrounding the death."

The killer, who shot Billy with a pump-action .22 calibre rifle, also made off with $40,000 which has never been recovered.

"A man was charged in 1998, however, no one has ever been convicted," the NSW Police spokesperson said.

A $100,000 NSW Government reward is still available for information that leads to the arrest and conviction of whoever is responsible for Billy's death.

Anyone with information should contact Crime Stoppers on 1800 333 000. Billy was in Year 12 preparing to sit his HSC when his life was tragically cut short.

In the wake of his death, friends described him as "a bloody good kid" with a cheeky smile. He loved basketball and tennis.

Billy had dreams of attending the University of New England where he had applied for early entry to study primary school teaching.