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In 1975, an 18-year-old set off hitchhiking from Hamilton to surprise her family in Hastings but she never made it.
Police are still trying to find Mona Blades' killer 43 years later. Now however, they have fresh eyes, new ideas and a totally different theory, and her family are hopeful there will be answers.
This is one of four New Zealand cases that could finally be on their way to being solved, thanks to a TVNZ series debuting this Sunday.
Cold Case is narrated by Seven Sharp's Hilary Barry, who describes the show as being "like Police 10/7 on speed".
As well as the Mona Blades case, it takes on the unsolved cases of Kayo Matsuzawa, whose naked, decomposing body was found in an Auckland stairwell cupboard in 1998; Dunedin mother of three Tuitania (Tania) Barclay, who disappeared in 2002; and Do Trieu, who went missing in 2008 and whose case is now being treated as a murder after being reopened in 2013.
For lovers of true crime, Cold Case really brings the genre close to home, giving viewers insight into real investigations, which have input from forensic pathologists, entomologists, DNA specialists, criminal profilers and more.
"It's an amazing opportunity to go behind the scenes to see a genuine police review," says Harper. "We're in this climate where we see so many American crime dramas - the CSI type things - where everyone's just walking around with a pen torch so they can find one tiny little clue that solves the whole thing within the hour.
"In reality, it's nothing like that. This is a genuine review, so I hope the viewers get excited to see how the layers get peeled back and see there's a wonderful and amazing opportunity to be part of an investigation."
Viewers are supposed to be a part of the investigation; Cold Case doesn't necessarily offer answers, but it does offer new information and based on that, asks the public to fill the gaps.
"It's very much a call to action," says Harper. "Sometimes it's a very specific call; were you this woman? Do you recognise this sort of predatory behaviour? Sometimes it's more generic."
Harper says Cold Case has taken three or four years to get from concept to screen, with much of that time spent working with police to find the right cases. They wouldn't use cases unless they thought a new investigation could actually lead somewhere, so for every case they investigated, Harper estimates there were another 10 they discarded.
That wasn't just for the sake of good TV; it was as much to protect the victims' families and the officers involved.
Hilary Barry says what struck her was the "tenacity" of the police officers who worked on the original cases and returned for the show.
"Take the Mona Blades case - even though that was 43 years ago, Stewart [Guy, the original detective] still thinks about it every day and has not let it go," Barry says.
"That's the thing that we forget - the news cycle moves on to a different story, but for the family, of course they never forget and neither do the cops. Even though it just seemed like there was no way of solving it, the police involved just were not going to give up and that's so cool."
According to Harper, new information is uncovered in every case and in one in particular, "there's a very good chance" that information and a new person of interest could "go a ways towards solving it".
Of course, it's a massive leap between a TV show and a successful arrest and prosecution, but both Harper and Barry are hopeful New Zealand's two degrees of separation could help.
Barry says: "The thing is, New Zealand is such a small place that everyone knows everyone else, everyone knows everybody's business, and all you need is one little memory to come back for somebody to be able to provide that last piece of the puzzle."
What: Cold Case
Where: TVNZ 1 and TVNZ On Demand
When: Premieres Sunday, 8.30pm
Help: If you have information that could help, call Cold Case: 0800 2653 2273