"He can't tell them anything new," he said.
"He told them everything he knew back then."
John Norsworthy said the pain of losing Furlong may explain why his son had refused to speak to police.
"I would imagine 20 years ago it was a painful experience and he didn't want to go through it all again."
He said he was confident Danny had nothing to do with her disappearance.
"On occasions he spoke to us about Jane but it's all a mystery to him, as it is to everybody else."
John Norsworthy said it had been "incredibly difficult" as parents but they had always supported their son.
They adopted Danny as a 4-year-old and had endured some difficult times with him.
He went to top private school St Kentigern's in an attempt to improve his behaviour but lasted only one term. He left home as a teenager.
"It was an attempt to put him in an environment that was good for him but he only lasted a term.
"They asked us to withdraw him."
Norsworthy and Furlong have a child, Aidan, who was only a few months old when she went missing in 1993.
Aidan, now 20, is cared for by John and his wife Beverley, who is the associate dean at Bethlehem Tertiary Institute in Tauranga.
"We've had to live with it and get on with life," said John.
Detective Senior Sergeant Paul Newman, second in charge of Operation Darlia, said the content of the police conversation with Norsworthy was "privy to the Operation Darlia investigation team".
"We would welcome further, more in depth discussions to progress the investigation."
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