Detectives were given the woman's details in June, but failed to make contact with her until November (file photo).

Police are defending their investigation into a senior officer accused of sex crimes as it emerges one of his potential victims fell through the cracks for five months.

Detectives were given the woman's details in June but failed to make contact with her until November.

During that time, they told others she had not responded to their repeated attempts at contact. However, that later proved to be untrue.

It emerged two detectives each thought the other had been attempting to make contact, when neither of them had.

READ MORE:

* Sex abuse case against senior Northland police officer heads to Crown solicitor

* Northland police 'ignored' letter raising sex concerns against senior officer

* Woman claims senior Northland police officer harassed and abused her for years

* Woman speaks out over explicit texts, allegedly from police officer

Tauranga lawyer Craig Tuck, who is in contact with the first alleged victim who came forward, said the bungle was "not a great start" to the inquiry.

"These are serious allegations about a senior member of the police force, and there's certainly a lack of confidence at this point in the investigation," he said.

Tuck questioned how detectives could make what he called a basic mistake.

"It seems odd that police are throwing what they say is a great deal of resource at this, but are unable to communicate between themselves to interview someone."

Email correspondence provided to Stuff showed the detectives maintained until October they had "tried to make contact", but received "no reply".

A month later, detective sergeant Nicola Reeves acknowledged there had been a "breakdown in communication" and took responsibility, as police backtracked on their earlier claims.

Detective inspector Darryl Sweeney said police were "limited in what we can say at this time" because it was part of an active investigation.

"These types of complaints can be very complex but we want to assure the community that we take service to victims very seriously and work as quickly as we can with the information available to us," he said.

The Independent Police Conduct Authority (IPCA) has been notified, according to further internal correspondence received by Stuff.

In an email, IPCA investigator Andrew MacNeill wrote he was "particularly concerned" if police had failed to get in touch with a victim who was expecting contact, and said the authority "would want to look into this".

It's not the first time concerns have been raised about police handling of the case.

The first woman to come forward said last month she was frustrated and anxious about how things had progressed, and worried at times detectives were not taking her complaint seriously.

Police launched a criminal investigation in April following her complaint to the IPCA.

In it, she alleged the senior Northland officer brought her flowers and nicknamed her 'Spice' before sexually abusing her multiple times over several years.

She said the alleged abuse had left her deeply traumatised, suicidal and depressed, and unable to enjoy a full sexual relationship with her current partner.

Detectives have spent the past six months building a potential case against the officer and have now referred their investigation to the Crown solicitor, who will decide whether to press charges.

For legal reasons, Stuff cannot reveal the identity of the officer under investigation.

The IPCA is also conducting its own investigation into the alleged sex offences.