Evelyn Greenup's aunt, Michelle Jarrett.

Still seeking answers: Evelyn's aunt, Michelle Jarrett. Photo: Janie Barrett

It was about 5am when Michael Scafidi and Greg Innes spotted a body, slack and motionless, in the middle of the road. Their truck lurched to a stop on a left-hand bend, metres from what looked like a teenage Aboriginal boy. He was, Mr Scafidi said, lying like a chalk outline "in one of those cop shows".

"He had his sloppy joe tied around his waist, he didn't have much facial hair. He looked like he was either asleep, drunk or dead."

Twenty-three years on, that odd encounter on a remote road in northern NSW holds what some say is the key to convicting an alleged serial killer.

Clinton Speedy.

Waiting for justice: Clinton Speedy. Photo: Supplied

Police, legal experts and the victims' families say they know who murdered Colleen Walker-Craig, 16, Evelyn Greenup, 4, and Clinton Speedy-Duroux, 16, in Bowraville in the early 1990s.

But they claim a dispute over the definition of a single word in the NSW Crimes Act is preventing the case from going to retrial.

Detective Inspector Gary Jubelin, who has worked on the case since 1996, said the families "have been let down by the justice system".

Evelyn Greenup.

Killed in Bowraville: Evelyn Greenup. Photo: Janie Barrett

"I have been investigating crimes for 20 years and I am still shocked by the lack of interest that has been shown in this matter," he told a NSW upper house parliamentary inquiry this month.

"We know who is responsible for the serial killing of three children but that person has not been brought to justice."

The children disappeared from the same road over a five-month period from September 1990.

Jay Hart, a white man who was close to the indigenous community, was tried for two of the crimes but acquitted. He was also a suspect in Colleen's murder, but her body has never been found.

According to Mr Scafidi, a stocky white man was standing over the body as they rounded the bend. His description of the two figures appeared to match that of Mr Hart and Clinton.

They stopped and said to the man: "'We could have run him over, we've got to get him off the road. Do you want a hand?'" Mr Scafidi recalled. "He said, 'No, no, I've already rung the police.'"

It was not until later, after hearing news that a young Aboriginal male had been found dead in bushland, that the men, who were meat delivery workers, reported the encounter to police.

The lead was not fully explored - one of a series of errors that thwarted the initial police investigation. The evidence re-emerged years later, but has not been heard by a court.

In 2012 the children's families asked then attorney-general Greg Smith to apply to the Court of Criminal Appeal for a new trial, which would lead to all three murders being heard together.

Detective Inspector Jubelin says subsequent investigations have uncovered significant coincidences that link all three murders and tie them to Mr Hart, who has changed his name.

He compared the case to that of convicted serial killer Ivan Milat, where all seven murders were heard in one trial.

"I can say on good authority that if Ivan Milat's trials were separated, there is a strong likelihood that he would be acquitted of all the offences and perhaps be walking the streets," he said.

Mr Smith refused the application. Among the reasons, he cited advice that an acquitted person can be retried only if there is fresh and compelling evidence which has not already been "adduced" in court.

The legal debate hinges on whether adduced means "tendered" or "admitted". Some evidence the families believe warrants a retrial has previously been tendered in court, but not admitted. Clarifying the definition would improve the likelihood that a retrial would be allowed, and the delivery men's evidence could be heard.

The legal disagreement is not the only roadblock the families have encountered - aside from the initial investigation, Detective Inspector Jubelin says they have suffered racism and disrespect at the hands of authorities.

Evelyn's aunt, Barbara Greenup-Davis, says the inquiry, established after a motion by Greens MP David Shoebridge, has given the families renewed hope. "Our hearts carry the scar of murder. I've been crying for 23 years, and we're still crying," she said. "To live through a retrial would be emotionally devastating for all of us. But does this little girl not deserve justice?"