The police watchdog has cleared an officer of wrongdoing hours before a murderer claimed his second victim.
Paul Tainui was on parole for the 1994 murder and torture of Kimberly Schroder when he was found over the limit at a checkpoint two-and-a-half years ago.
He had knives in his boot but police let him go on foot and secured his car.
Tainui took a taxi to the home of his next victim, 27-year-old Nicole Tuxford, waiting eight hours for her to return home, where he raped and murdered her.
The Independent Police Conduct Authority (IPCA) has found there was a lack of mechanisms or training for officers to identify when a parolee needs to be arrested and considered urgently for recall to prison.
But the watchdog says there's no certainty the murder could have been prevented if better systems were in place, finding it was reasonable the officer didn't detain or arrest him.
"The officer's decision to summons rather than arrest Mr Tainui for his drink driving offence was in keeping with standard police practice," the IPCA said in a statement.
"When Mr Tainui volunteered to the officer he had knives in his car, the officer accepted his reason for having them and requested he leave them in his locked car boot, which he did."
The IPCA said the officer believed Tainui's explanation for having the knives in his car was "reasonable". The Department of Corrections has since worked with the police to ensure a better system, the watchdog said.
"There were no clear processes in place at the time for him to follow in respect of parolees and nothing in the law to require that life parolees be arrested when suspected of committing an imprisonable offence," authority chair Judge Colin Doherty said.
In response to the IPCA report, police said Tuxford's murder was a tragedy and her family remained in their thoughts.
"Our thoughts remain also with the family of Kim Schroder, who was murdered by Tainui in 1994, for the horrendous re-traumatising they faced following Nicole's murder," Canterbury District Commander Supt John Price said.
He said the officers who released him from the checkpoint have been deeply affected by Tainui's "despicable" actions.
"While the IPCA has emphasised that there is no certainty Nicole's death would have been averted if the enhanced notification system had been in place, police and corrections have worked hard to develop an improved process in order to protect the public and to support front-line officers, and will continue to work together to appropriately manage offenders on parole."
Speaking to Newshub last year, Tuxford's mum Cherie Gillatt said she wanted justice for her daughter.
"They had him in their hands, they processed him," Gillatt said.
"He was a convicted murderer and he had knives in his car.
"You just can’t let somebody go on like that. You've got to dig deep."