Colleen Walker, 16, vanished from Bowraville in September 1990, after travelling there from Sawtell to go to a party and stay with friends.

On September 14, the day after the party, she was due to catch a train to go on a two-week trip, but she never arrived at the station.

Crown prosecutors allege she was killed by the same man accused of murdering Clinton Speedy-Duroux, 16, and Evelyn Greenup, 4, in Bowraville in late 1990 and early 1991.

The man, who cannot be named, was acquitted of the murders of Clinton and Evelyn in separate trials. The NSW Attorney-General is attempting to overturn the acquittals in the Court of Criminal Appeal, so the three cases can be heard together for the first time.

The appeals bench must find there is "fresh and compelling evidence" for a retrial to be ordered.

On Monday, as the hearing entered its fourth day, the man's legal team said Colleen could have been taken by "any number of strangers" who were in the area for a football competition at nearby Macksville.

"Any number of strangers, or out-of-towners, (were) in town for the football," defence barrister Julia Roy said.

Colleen's clothes were fished out of the Nambucca River seven months after she disappeared, in a bag weighted down with rocks.

Her body has never been found, however, a Coroner ruled after a 2004 inquest that she is dead.

Ms Roy said two pairs of underwear were found in the bag in the river, meaning the clothes may not have been what Colleen was wearing when she disappeared.

"There is an available inference that it was the bag she packed, or at least it included the bag she packed (to go on holidays)," Ms Roy said.

The Crown alleges there is a sexual link between the murders, with all three children disappearing after incidents where women's pants were pulled down in the middle of the night.

Ms Roy said it was "extreme" to suggest someone would resort to murder if they were discovered touching a sleeping woman.

She argued that evidence about Colleen's disappearance became "contaminated" when residents gathered to talk about where she had gone, which left some confused about what they had seen themselves and what they had heard from others.

Another "egregious" contamination was seen at the 2004 inquest, Ms Roy said, where witnesses were encouraged to stay to watch each other's evidence.

"It diminishes the reliability and probative force of later evidence," Ms Roy said. "It gives rise to prejudice."

Defence barrister Mark Ierace, SC, said the case will act as a test of the Crimes Appeal and Review Act, which allows a person's acquittal to be quashed and a retrial ordered.

Though the legislation has operated for 10 years, the Bowraville case is the first application to be made using it, Mr Ierace said.

The hearing continues.