"The issue in this case, one of the things that will be front and centre, is the confessional material... the issue will be whether you find that reliable," Mr Krebs said.
"I say to you from the outset: it's false, it's a cobbled-together story."
He said the idea of someone admitting a crime they had not committed might be difficult for the jury to grasp, but there had been well-publicised cases in New Zealand and abroad where exactly that had happened.
"What if a person didn't commit the crime but knew enough about the crime to give a plausible narrative?" he said.
"What if immense pressure was put on them to confess in circumstances that led them to believe there would be no consequences?
"At that point the gold-plating of a confession effectively falls off. The counterintuitive proposition [of admitting a crime he did not commit] becomes eroded."
Mr Krebs said the six-month undercover operation, of which Reddy was the target, was effectively "grooming".
It was the first of its kind to be heard by a jury in this country, he told them.
"Immense pressure was put on him to front up with information, and that's what he did," the lawyer said. "He was groomed to believe there would be no consequences, only benefits."
Mr Clancy told the jury they would see and hear recorded conversations, in which Reddy told undercover officers how he killed the victims, and hid their bodies in a muddy grave under the Takapuna overbridge.
"What you will see is a man unburdening himself of a terrible secret that he's carried with him for years.
"Pouring out details that only the person who murdered Pakeeza and Juwairiyah could have known."
The trial, before Justice Raynor Asher and a jury of four men and seven women, is scheduled to run for four weeks.
