Instead of bringing him a phone, Manukau police officers brought him a device which held a 21-second recording.
"Hi Kamal, this is [X] here. [X] isn't my real name. I'm actually an undercover police officer and I've been working with you for a number of months now in relation to the disappearance of Pakeeza and Jojo."
Reddy made no comment and was led back to the cells.
The officer's name is suppressed, as are the names - both real and fake - of all police staff in the Operation Canvas investigation.
All that the media can report is that the inquiry involved an officer being introduced to the defendant and gaining his trust through a series of "simulated criminal scenarios".
The details were suppressed after police raised concerns publication might jeopardise any future operations and the safety of undercover officers.
This case is the first time a New Zealand jury has heard specifics of the technique.
A hearing to review the suppression order takes place next week.
Police said they resorted to undercover investigations only when all other options had been exhausted.
Reddy's being Ms Yusuf's most recent known partner put him under the microscope immediately. And when they found he had previously been charged with threatening to kill her, that scrutiny intensified.
What they did not know at that stage was that while Reddy stood in the dock at Manukau District Court accused of domestic violence in early 2007, she lay in a muddy grave under a motorway bridge.
At their Otara home on November 11, 2006, the now 43-year-old flew into a drunken rage, accusing Ms Yusuf of being unfaithful to him.
She was so scared she contacted her ex-husband, Mohammed Faizal - the father of her daughter Jojo.
When he arrived at the Clarkson Cres address he was confronted by Reddy brandishing a 50cm machete.
He swung the weapon and missed Mr Faizal but was charged with assault with a weapon and two counts of threatening to kill.
On January 22, 2007, Reddy appeared in court where he admitted the machete charge.
What he did not admit was that days earlier he had strangled Ms Yusuf to death in her sleep and smothered her child with a pillow.
He kept their bodies in the boot of his car for a couple of days and then unceremoniously dumped them in a hole under the cover of darkness.
The charges of threatening to kill were withdrawn because Ms Yusuf could not be found for police to speak to her.
Reddy spent weeks following the murders getting rid of anything that could tie him to the victims.
He put their clothing in recycling bins and dumped a mattress in skips, returning days later to ensure they had been emptied.
And during all that, he completed an anger management course while on bail.
When Reddy returned to Manukau District Court in June 2007, he was discharged without conviction.
Nearly nine years later, before the High Court at Auckland yesterday, there was no avoiding conviction for the most serious of crimes.
It took a jury four-and-a-half hours to reach unanimous verdicts.
He will be sentenced next month.
