In 1992 Amber-Lee Cruickshank vanished at Kingston near the southern end of Lake Wakatipu.
Despite exhaustive searches, there has never been any sign of the 2-and-a-half-year-old.
Last week the Herald launched Chasing Ghosts, a six-part podcast series, news feature and mini-documentary about Amber-Lee's disappearance and the aftermath.
Chasing Ghosts marks the 25-year anniversary of the toddler going missing.
Despite more than 52 years of investigations authorities cannot shed any light on what happened to little Betty.
Police are now preparing to officially close the case and refer Betty's disappearance to the coroner.
Betty was the daughter of farm workers Charlie and Marion Wharton, who were considered suspects in her disappearance for many years.
They were both sent to prison after the death of Betty's older sister, convicted with failing to provide the necessaries of life.
When Betty was born the couple were being monitored by authorities, but because they moved around a lot for work they fell through the cracks.
And when child welfare workers eventually located the Whartons, Betty was no longer with them.
The couple told police Betty was in the care of her grandfather, but later changed their story to say she had been informally adopted by a Te Awamutu woman named Martha.
"In spite of the isolation, in spite of there not being lots and lots of people around, how a 2-and-a-half-year-old girl can go missing in daylight is just baffling."
Walker and the current officer in charge of the case believe Amber-Lee was taken, killed and her body disposed of.
"The most likelihood is that somebody has taken her, somebody is involved and there is somebody out there who knows that," Walker said.
Chasing Ghosts tells Amber-Lee's story in unflinching and enormous detail. It was researched and written by senior crime reporter Anna Leask.
Visual journalist Mike Scott did the field recording and produced the mini-documentary.
Leask said the project aims to bring fresh attention to the case in the hope that someone comes forward with information that could help bring Amber-Lee home.
If you know what happened to Amber-Lee, or have information you have never shared with police that could help the investigation, please come forward. Contact Detective Sergeant John Kean at the Invercargill police on 021 191 5321 or email john.kean@police.govt.nz.
To pass on information anonymously, contact Crimestoppers on 0800 555 111 or fill out their online form here.
This service is completely confidential and you do not have to reveal your identity. Police have no way of tracing who passes on tips to Crimestoppers.