John Hope Muchirahondo, 38, was found guilty of 17 counts of rape and sexual assault on Monday.
He was also found guilty on one count of not providing access to a cell phone. The offending took place in Christchurch and Auckland, spanning from 2011 to 2021.
Detective Inspector Nicola Reeves told Morning Report she would have liked guilty findings on all of the charges but was pleased with the result.
Many police staff had lived and breathed the case for the past four years, she said.
"Whilst that's our side of things, you've got to think about all of these complainants who are waiting for their moment in court as well so it's hanging over their heads the entire time."
Reeves said sexual assault cases can be difficult to investigate and prosecute, but she had nothing but praise for the women involved.
"Even just picking up the phone to ring the police and tell us something that you might not be sure what happened, or you're just so wishing it hadn't happened, and then you're going to tell a total stranger, you're going to do an interview, then if we're prosecuting you've got to wait the time frame to get to trial and then you've got to go to court and essentially sort of say it all again, and have your credibility challenged, you're having your memory challenged.
"It's a journey, but these women are really supported to do that and they've amazing, they've stood up to it, they've said what happened and they've been believed, their strength is incredible."
Police initially began investigating a couple of recent assaults and then the operation "just grew legs" as more people came forward, or were suggested for police to speak to, Reeves said.
And while the trial and jury deliberation were lengthy, she said that wasn't a surprise.
"They've essentially been working through 15,16 mini trials within one trial."
