A judge has for the second time urged convicted killer Leslie Alfred Camilleri to reveal where he buried 13-year-old Prue Bird's body.

Supreme Court Justice Elizabeth Curtain, who at an earlier hearing told Camilleri to "exercise his conscience" and reveal Prue's whereabouts, said on Monday now was the time to do the right thing and tell police where the schoolgirl's body could be found.

She said detailing Prue's whereabouts would be a powerful indication of his remorse over the 1992 murder.

Prue Bird.

Outside court, Prue's mother, Jenny, who has long pleaded for Camilleri to tell her where her daughter was buried so she could lay her to rest, said she turned to the convicted killer in the dock and mouthed the word "please" to him before he was led away. Camilleri did not respond.

A witness had earlier told the court how she saw convicted Russell Street bomber Craig Minogue outside Prue's Glenroy home on the day the 13-year-old was abducted and murdered.

The witness, who can only be identified as Witness L, said on Monday she was 18 and walking home eating an ice-cream when she saw two men, including one she believed was Minogue, standing outside the front door of Prue's home on February 2, 1992.

Witness L said she saw Prue later being driven away by the men.

She had earlier seen either a gun or a mask with the face of a president in the car.

Police have alleged in a previous court hearing that the motive for Prue's abduction and murder revolved around payback over police statements made against the men who bombed the Russell Street police building in 1986.

Prue's grandmother, Julie, and her partner, Paul Kurt Hetzel, gave statements to police about the fatal bombing.

Camilleri had pleaded guilty to murdering Prue but is disputing parts of the Crown case. He claims he acted alone when he killed Prue.

Police believe Prue was killed between the day she was abducted and when Camilleri was arrested interstate on outstanding warrants nine days later.

Camilleri, 43, is serving two life sentences for raping and murdering Bega schoolgirls Lauren Barry and Nichole Collins in 1997.

Prue has not been seen or heard from since February 2, 1992, and her body has never been found.

Her mother, Jenny, left home that morning, leaving Prue with a family friend who also lived at the house.

Prue was last seen in the kitchen preparing lunch. When the friend returned to the house after packing boxes in the garage, the front door was open, the television was on and a hot meal was sitting uneaten on a table.

Witness L told the court she waited 18 years before deciding to go to the police to reveal what she had seen because she had previously had no self confidence.

She said two cars were parked near Prue's home the day she disappeared and she wrote down the number plate of one of the cars and stuck it on the fridge. As the two men stood in front of Prue's home, another man sat in the second car smoking.

Asked why she had taken down the number plate, Witness L said: "Something made me think I was in danger."

She later told her family what she had seen but they did nothing.

Witness L only decided to come forward because she said she felt Prue's presence, and the schoolgirl was telling her to do something.

During a session with a hypnotist, Witness L claimed one of the men looked like Craig Minogue.

Witness L said when she saw Prue being driven away, she thought she was being taken to see her grandparents.

"You don't think your friend is going to be kidnapped," she said.