This "unquestionably had a devastating impact on his victims", Assistant Police Commissioner Malcolm Burgess said today.
The Independent Police Conduct Authority (IPCA) has today released a report that found police failed to properly investigate a sexual attack on a woman, known as Ms A, in 1987.
The police investigation into Ms A's complaint "did not meet the expectations of policing even at that time", chairman Sir David Carruthers said.
Failures included not taking a statement from Ms A, who identified Rewa as the offender, and not attempting to make any inquiries to corroborate or call into question the alibi given by Rewa at the time.
Mr Burgess apologised to Ms A, "who police clearly failed at the time by not properly investigating information she supplied identifying Rewa''.
"Whilst I consider there was no lack of will amongst those officers involved at the time to catch the person responsible, it is clear from this detailed report that more should have been done in aspects of some of the early investigations.
"We accept that and apologise to victims affected by those failings.''
But Sir David said even if the complaint was properly investigated, there was no evidence Rewa would have been captured any earlier.
"Although some faults have been found by the authority concerning the series of investigations into offending by Malcolm Rewa, it is not clear that any of these would have led to Mr Rewa's arrest, successful prosecution or earlier identification as the serial sex offender.''
Last year TV3's 3rd Degree programme suggested police overlooked Rewa's involvement in six incidents, including three sexual assaults, at addresses in London St, Ponsonby.
But Sir David said Rewa operated across a number of police districts and there was no sharing of information between the districts at the time.
"Police work at this time was primarily paper-based and it is unlikely that traditional methods of policing could have uncovered the operation of a serial sex offender, across districts, earlier.''
Today, policing of sexual assault cases was approached in a different manner with improved education, training and resources, he said.
He made no recommendations to the police to improve their procedures.
Another complaint investigated by the IPCA was that police withheld information from Teina Pora's defence team during his first trial for Ms Burdett's murder.
Sir David said there was no evidence that happened.
Ms A was the first known victim in a string of 25 attacks by Rewa during a nine-year period.
Ms Burdett, an Auckland accountant, was raped and murdered in her Papatoetoe home in 1992. Pora, then aged 17, was convicted of her murder in 1994.
He was found guilty again at a retrial in 2000, which was ordered after the semen in Ms Burdett's body was found to belong to Rewa.
Pora's case will go to the Privy Council.
Susan Burdett's brother Jim said he would take time to read the full report thoroughly before deciding whether to make any comment.
Timeline
* 1987: Ms A makes a sexual assault complaint to police.
* 1987-1996: Years spanning Rewa's offences.
* May 30, 1998: Rewa convicted on multiple sex charges dating back to 1987.
* July 3, 1998: Sentenced to preventive detention with a minimum non-parole period of 22 years.
* January 20, 1999: Convicted for the sexual assault on Susan Burdett and sentenced to 14 years.
