The Marie Jamieson homicide is the first time in New Zealand that a long-standing murder case has been solved by identifying a suspect through the DNA of a sibling.

Joseph Martin Reekers yesterday pleaded guilty in the High Court in Auckland to murdering the 23-year-old hairdresser in 2001.

His plea ended eight years of police investigation and spared Ms Jamieson's family the ordeal of a trial.

The Herald can reveal that Reekers became a "person of interest" after police used new technology last year to retest the DNA sample found on Ms Jamieson's body.

A search of the DNA database did not find a direct hit, but police then ordered a familial DNA test, which identifies similar genetic traits, such as those of a relative.

This identified a sibling of Reekers who had a criminal record.

Further inquiries into the family identified Joseph Reekers, who lived in West Auckland - where Ms Jamieson was found - and had a conviction for rape.

Then in April last year, Reekers was caught stealing an $8.20 roll of salami from the Henderson Pak'n Save supermarket.

He was convicted of theft, and the conviction allowed police to issue a compulsion order to take a DNA sample from him.

When tested, it matched a sample found with Ms Jamieson's body.

Under the Criminal Investigations (Bodily Samples) Act, police can issue an order after a person is convicted of offences such as theft, rape and arson.

It is understood Reekers reluctantly complied with the order in June last year, shortly before his arrest was announced.

Police spokesman Grant Ogilvie confirmed that 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.

But the technique was used to secure the conviction of Wayne Robert Jarden, 50, in the Christchurch District Court last December for rapes in 1988 and 1996.

The new technology enabled police to run a familial DNA search which isolated two relatives of Jarden and revived interest in a man who had previously been regarded as a 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, and a voluntary sample which he gave confirmed the match.

Yesterday, Reekers pleaded guilty in the High Court at Auckland to murdering Ms Jamieson, ending one of the city's most mysterious murders.

The 23-year-old 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.

Her father, Gerry Jamieson, was in court for the guilty plea yesterday. He said his family feared being subjected to the tactics used by Clayton Weatherston in his murder trial.

Weatherston was found guilty of murdering Sophie Elliott, but her parents had to listen as he blackened her reputation during the trial.

"After the way Sophie Elliott's family were treated in her trial ... we found that appalling," Mr Jamieson said. "That goes through your mind, that the same thing could happen to us.

"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 a degree of closure to Ms Jamieson's family, who had been left wondering for years what had happened to their daughter.

Mr Wood said Reekers was not one of the original suspects in the investigation, but declined to discuss the DNA trail that led to him until after he is sentenced on April 20.

"With homicides, we have a very good record of resolution and we don't give up," he said. "With the passing of time and technology [improvements], it is becoming easier."