Police investigating an Auckland cold case have offered a reward of $50,000 and immunity from prosecution for information that leads to a conviction in the death of Jane Furlong in 1993.
Ms Furlong, 17, was last seen on Auckland's Karangahape Road in May of that year and her disappearance had been considered a cold case until her remains were found in dunes at a Port Waikato beach in May 2011.
The discovery led to police excavating the back yard of her Onehunga home, but they would not say whether they had found any items of interest.
Detective Inspector Mark Benefield says a number of people, including Danny Norsworthy - Miss Furlong's partner and the father of her baby - are refusing to be interviewed.
Mr Benefield told Checkpoint on Thursday that Miss Furlong had compromised herself in the eyes of others by giving evidence to police and those people are significant to their investigation.
He says an associate of the killer who transported or buried her body could be offered immunity and that, coupled with a reward, may induce someone to come forward.
The young mother worked as a prostitute at the time she went missing. Last year, police asked for her clients in May 1993 to contact them.
They also appealed for a man Miss Furlong had named in her diary as Tommy to come forward.
Police have said they believe more than one person was involved in her death.