Kamal Reddy told undercover police officers information that only the killer could have known, the Crown says.
Mr Reddy denies charges of murdering Pakeeza Yusuf and her three-year-old daughter, Juwairiyah Kalim, in 2006 and burying their bodies under a motorway bridge on Auckland's North Shore.
He told jurors at the High Court in Auckland that Ms Yusuf's new boyfriend was the real killer.
But the Crown said Mr Reddy was a violent man who had alcohol issues and beat Ms Yusuf. He grew jealous and murdered Ms Yusuf when he believed she was seeing another man.
Crown prosecutor Natalie Walker said Mr Reddy led officers to the very spot under the motorway bridge in Takapuna where police later found the bodies of Ms Yusuf and her daughter - eight years after they went missing - and posed for a photograph on the spot.
Mr Reddy described to undercover police officers how he took hours to dig the hole to his height and that he used stones in the backfill to prevent erosion. Police found stones in the grave fill.
Mr Reddy also told officers what the pair had been wearing. That included pants and a jumper for Ms Yusuf and a nightie for her daughter.
Remains of clothing were found in the grave and are consistent with what he described.
He also said they were not wearing shoes and no shoes were found in the grave.
Under cross-examination from Ms Walker, Mr Reddy said it was not him who had carried out the killing but Ms Yusuf's new boyfriend James.
Storage unit questions
Ms Walker also questioned him about a storage unit he paid for soon after Ms Yusuf disappeared.
The Crown's case is that after carrying out the murder, Mr Reddy slowly moved Ms Yusuf's possessions, including furniture, to the storage unit.
He also dumped some of her belongings at construction sites around Manukau.
That evidence comes from what Mr Reddy told undercover police officers who befriended him and invited him to participate in a series of staged criminal activities, which he believed were real.
Under questioning from Ms Walker, Mr Reddy denied that was the case and said he made up the story.
He said he was using the storage unit for storing his mechanics tools.
Ms Walker questioned Mr Reddy about Ms Yusuf's money going missing after she died and took him through Ms Yusuf's bank records.
They showed her single mother's benefit of over $400 a week was going into her account and someone was continuing to withdraw money after she disappeared.
Ms Walker said Mr Reddy had told police earlier that he knew Ms Yusuf's pin number and also pointed to a lack of activity in his own account and asked him if he had been living off Ms Yusuf's benefit.
Mr Reddy said that was not true.
He was asked why his name was on a Sky account for Ms Yusuf's home, if he was not living there.
He said he did not know how his name got on the document, and later said that he had set that up for Ms Yusuf and her new boyfriend James.
Today the jury will hear closing addresses from the Crown and defence before Justice Asher sums up the case and the jury retires to consider their verdicts.