Police have cleared a top NZ Rugby staff member of allegations he was a mobile phone sex pest.

The determination ends a six-year saga, which includes a botched police investigation that saw mobile phone records gathered illegally.

The move damaged the investigation so badly police halted further inquiries and apologised to the two women who complained about the unwelcome texts, and to the NZR staff member mistakenly linked to the messages.

But allegations continued to swirl, and NZ Rugby was forced to order an urgent, high-powered inquiry after they were published late last year.

NZ Rugby chairman Brent Impey told the Herald on Sunday he had spent 10-12 hours a day leading a "top priority" investigation.

"I am now of the view [the staff member's] reputation has been very unfairly potentially damaged by all of this."

Publication of details from the police inquiry in the NZ Listener magazine last October spurred him to root out the truth "whatever the result was".

The story detailed evidence gathered by the police revealing the staff member as the sole suspect in an investigation into repeated unwanted text messages sent to two women in 2011. They later complained to police.

Impey said NZ Rugby's board wanted a definitive answer to the allegations, ordering multiple legal reviews.

He said a key piece of evidence emerged that strongly argued against the staff member being the mystery texter, because he did not attend a meeting linked to one of the text messages.

The police evidence - viewed by the Herald on Sunday - showed a 2Degrees mobile phone bought off-the-shelf with no subscriber details was used to text the two women in 2011.

The first woman to receive texts was a Wellington real estate agent, but the first complaint to police came from a staff member working for the company running the Rugby World Cup.

She received her first unsolicited text message from the same phone. The message included details strongly suggesting the mystery texter had been with the woman in a Rugby World Cup meeting - along with more than 40 others - in Auckland that day.

The text read: "I've been looking at your long legs all afternoon and it is lucky you are not my team services manager."

Impey said the NZ Rugby staff member had no connection to the World Cup or to the woman who received the text messages, and was not at the meeting. "Further, he was not even in Auckland when the meeting took place."

But the man's name emerged after police obtained the 2Degrees phone records without a search warrant. The officer who got the phone records then rang the only other number to which a text had been sent - the real estate agent.

According to the agent's statement to police, the constable told her the original complaint had come from a NZ Rugby staff member - not the Rugby World Cup company. The constable then nominated names until she recognised the accused staff member's name because she had shown him around a house.

When the real estate agent said she recognised the name, he became listed as the sole suspect on the police file. His name was circulated among Rugby World Cup staff, and word eventually found its way to NZ Rugby.

Impey said knowing the accused man "wasn't in the city at the time" was one of the reasons that led to the board's support.

"The inquiry is over. There is complete satisfaction no NZ Rugby staff member was involved."

Detective Sergeant Max Taylor said mistakes were made investigating the messages and the inquiry had gone no further. The errors included unlawfully gaining access to phone records and confusion over the difference between NZ Rugby and the Rugby World Cup 2011 company.

"Police have apologised to a NZ Rugby staff member who was mistakenly linked to the matter at one point. There was no evidence or information that any staff working at the NZ Rugby Union were involved."

He said the phone data was obtained without a search warrant and - even so - was "inconclusive and therefore highly unlikely to have been sufficient to progress the matter to a person of interest interview or to a criminal charge".

He said police had offered an apology to the women who had complained about the text messages.

NZ Rugby is preparing to make public its Respect and Responsibility Review, having launched the inquiry in the wake of a series of scandals that rocked the sport.

The Chiefs were the focus of an inquiry into allegations it hired a female stripper for a team function who was then sexually assaulted. It was the highest profile of a series of incidents that raised questions about the behaviour of those involved in rugby.