The sister of Tracey Ann Patient, who was murdered in Auckland 40 years ago when she was 13, says she will never be able to forgive the killer.
Police have reopened the cold case into Tracey Ann's death after new leads surfaced.
Her sister Debbie hopes the case will finally be solved and says what the killer did was unforgivable.
"What they did was wrong, it was very wrong, they took a child's life. However many years it's been, this person's had a life, probably got a family, you know he's running around happy as Larry. He's got off with murder," she said.
She added she would love to be able to say that she forgave her sister's killer, but says she couldn't do that.
"I don't forgive that person at all. I hope that person's had an awful, awful life. I really do!"
She continued: "I hope they've thought about if not every day, I hope it's been on the mind. And I would love for them to give themselves up."
Tracey Ann was walking home from a friend's house in Henderson in January 1976 and was just five minutes away from her parent's property when she disappeared.
Her body was found just metres off a path the next day by a man walking his dog.
She had been strangled with pantyhose.
Despite a large-scale investigation at the time of the murder, with police examining hundreds of potential suspects, it remains unsolved on the eve of the 40th anniversary of her death.
A team of eight detectives have been working full-time on the case since November last year after they came across new leads.
Detective Inspector John Sutton, who is overseeing the investigation, says police have opened new lines of enquiry with people as far away as Australia.
"Despite 40 years having passed, someone out there knows who did this," Det Insp Sutton said on Thursday.
"For 40 years, the Patient family have lived with the absolute trauma of what happened to their daughter and sister, they have never known who took Tracey from them or why."
A mystery caller contacted police 22 months after the murder and told them that a signet ring given to her by her boyfriend was in a rubbish bin outside an Avondale chemist.
It was recovered and it is believed Tracey was wearing the ring when she disappeared.
The anonymous person gave police the number 126040 and said he would call back later, which has prompted many conspiracy theories in the years since.
Two specialist investigators were seconded to the case in 2011 but couldn't make a breakthrough.
In the 40 years since the murder, more than 850 people have been profiled but no one has been charged.