Joseph Martin Reekers became a "person of interest" in the unsolved death of Marie Jamieson, which occurred in February 2001, after police in 2008 retested, with new technology, the DNA sample found on Ms Jamieson's body.
A search of the DNA database failed to find a direct hit.
Police then ordered a familial DNA test, which finds those with similar genetic traits, for example, a relative.
The second DNA test on the suspect sample identified a sibling of Reekers.
The sibling had a criminal record.
Further inquiries into the family identified Joseph Reekers, who lived in West Auckland where Ms Jamieson was found, and who had a previous conviction for rape.
From that point on, Reekers was a suspect.
In April last year, Reekers was caught shoplifting a $8.20 roll of salami from the Henderson Pak'n Save supermarket.
He was convicted of theft - shoplifting to a value of less than $500 - and discharged in the Waitakere District Court in April 2008.
The conviction allowed police to issue a compulsion order to take a DNA sample.
Under the Criminal Investigations (Bodily Samples) Act, police can issue an order after conviction for offences such as theft, rape and arson.
It is understood Reekers, after some reluctance, complied with the order in June 2008.
The subsequent hit matched a previously unknown genetic profile found with Ms Jamieson's dead body.
Reekers' arrest was then announced.
Police spokesman Grant Ogilvie confirmed familial DNA testing was used to solve the murder of Ms Jamieson.
It is the first murder in New Zealand to be solved in such a way.
The only other crimes to be solved with familial testing were two prominent cold cases in Christchurch, when Wayne Robert Jarden (50) was convicted in the Christchurch District Court in December 2008 of sex attacks in 1988 and 1996.
The new technology had allowed police to run a familial DNA search, which isolated two relatives of Jarden, and had reignited interest in the man previously regarded as a strong suspect.
Detectives began tailing Jarden again, and picked up a cigarette butt he discarded on the street.
The DNA from his saliva closely matched the evidential sample.
Jarden gave a voluntary sample, which matched the genetic profiles from the rapes.
Yesterday, in the High Court at Auckland, Reekers pleaded guilty to the murder of Ms Jamieson, and ended the case of one of the city's most mysterious murders.
Ms Jamieson (23) was last seen at a service station in Kingsland and her body was found nine days later, behind factory buildings in West Auckland.
DNA from an unidentified man was found on Ms Jamieson's clothing.
It was always a key focus of the police investigation.
But no arrests were made for more than seven years, until the familial testing identified Reekers as a suspect.
Ms Jamieson's father, Gerry Jamieson, was in court to hear Reekers' guilty plea yesterday.
After the hearing, Mr Jamieson said his family had feared being subjected to the tactics used by Clayton Weatherston in his murder trial.
Weatherston was found guilty of the murder of Sophie Elliott, but only after subjecting her parents to the indignity of listening to her former boyfriend blacken her reputation.
"After the way Sophie Elliot's family were treated in her trial . . .
"We found that appalling.
"That goes through your mind of course, that the same thing could happen to us," Mr Jamieson said, adding: "Obviously, a guilty plea means you don't have to go through a trial, which is a blessing for our family."
Reekers' lawyer, Chris Comeskey, said his client had been "tormented" since the day he killed Ms Jamieson.
"He told me there hasn't been a day go by where he hasn't thought about it and experienced huge feelings of guilt."
The officer in charge of the case, Detective Inspector Steve Wood, said the guilty plea would bring some closure to Ms Jamieson's family, who had been left wondering for so long what happened to their daughter.
Det Insp Wood confirmed Reekers was not one of the original suspects, but: "With homicides we have a very good record of resolution and we don't give up.
"With the passing of time, and technology [improvements], it is becoming easier."
Criminals should be wary as technology continued to become more advanced, Det Insp Wood warned.
"Who knows what might happen in the future," he said.
