The evidence from the nine-month inquiry was reviewed by the Crown Solicitor of Wellington before a decision was made this week to not pursue a criminal prosecution against Mr Gutry, who is married with children.
But there is no guarantee that the 48-year-old will return to his role as one of the most senior detectives in the region.
Mr Gutry faces an internal disciplinary inquiry which centres on why he looked at the woman's file on the police computer system, known as the National Intelligence Application (NIA), up to 20 times over two years. Unauthorised access to NIA has led to serious misconduct or criminal charges in the past.
The code of conduct process will also investigate whether the sexual relationship took place in work hours, which would breach police rules.
Mr Gutry's lawyer, Todd Simmonds, said the decision not to lay charges "is the clearest possible indication that the allegations made against Detective Inspector Mark Gutry had no substance".
"Detective Inspector Mark Gutry is obviously pleased with the outcome of the criminal investigation and his intention at this point in time is to return to police duties as soon as is possible."
The criminal investigation was launched when the woman wrote to Police Commissioner Peter Marshall last July after seeking help from Shannon Parker, who runs a police watchdog website.
The complainant could not be reached for comment yesterday, but Ms Parker said she had spoken to the woman, who was relieved the police had made a decision.
"She did the right thing coming forward and it took a lot of courage."
Despite no criminal charges being laid, Ms Parker said several matters relating to Mr Gutry's conduct have been identified, one of which was accessing the police computer system for personal use.
The complainant has previously told the Herald she waited three years to lay a complaint because she was a solo mother who felt "powerless" to speak up against a senior police officer.
She hoped his access to her file on the national police computer would be taken seriously. "He's looked me up 20 times in two years ... I'd love to know the reasons for that."
She was supported throughout the nine-month inquiry by Louise Nicholas, whose evidence launched a Commission of Inquiry into police sexual conduct, and is now an advocate for sexual abuse survivors.
Mr Gutry is an experienced and popular officer who was described by one source as the "right-hand man" for Counties Manukau district commander Superintendent John Tims.
Mr Tims said the allegations of inappropriate behaviour were treated very seriously but there was insufficient evidence to initiate criminal proceedings.
"We rightly expect high standards of behaviour from our staff and we have robust processes in place to deal with such complaints.
"We have looked at this complaint thoroughly from a criminal perspective and will now consider it under the Code of Conduct.
"We are also working closely with the complainant to keep them informed."
Mr Gutry remains suspended.
Mark Gutry
• Detective Inspector Mark Gutry is a senior officer in the Counties Manukau police district. Some cases he has been involved with:
• 2000 Dr Chris Simpson found guilty of the manslaughter of his elderly mother Marjorie who was terminally ill.
• 2005 Chinese woman Qing Zhao kidnapped from her Auckland home and held for $1 million ransom. Three men jailed for 10 years.
• 2010 Constable Jeremy Snow gunned down while on duty. Neshanderan Rajgopaul convicted of attempted murder.
• 2010 Super City candidate Daljit Singh arrested and later convicted for electoral fraud.
• 2012 Rae Portman kidnapped and murdered by Paraire Te Awa.
