In 2015, a married couple and their friend ventured into the remote goldfields of Western Australia. Only one of them came back.

Ray and Jennie Kehlet were a couple in love, chasing a dream of striking gold in Sandstone, WA. But their trip of a lifetime ended in tragedy. In one of Australia's most baffling cold cases, Ray was found dead at the bottom of a mineshaft, while Jennie vanished without a trace.

Their friend and colleague, Graham Milne, was the only survivor.

7NEWS Spotlight delivers the most in-depth analysis yet of a mystery that has haunted Australia for a decade. Reporter Liam Bartlett reveals shocking discrepancies in Graham Milne's story and uncovers new forensic evidence that police seemingly ignored.

7NEWS Spotlight also exposes a bombshell revelation from Milne's estranged daughter. In an exclusive interview, Sarah Hopkins alleges a violent past, painting a dark portrait of the man who walked out of the desert alive.

"Do I believe he knows more than he's saying? A hundred percent I do," says Sarah Hopkins.

Meanwhile, former ADF soldier and search volunteer Rick Heaton reveals he found critical evidence police missed, including a bullet casing and Ray's shirt buried in the mineshaft.

And be watching Sunday to see what 7NEWS Spotlight uncovers after commissioning its own independent testing by forensic expert Dr Dennis McNevin to analyse the evidence.

Liam Bartlett said: "This is a case that should have been solved years ago. The evidence was there. The questions were there. But the answers were ignored.

"We've spoken to the people closest to Ray and Jennie, and the one person who knew Milne better than anyone, his own daughter. What she reveals is nothing short of explosive."
 

On Sunday, 7News Spotlight addresses the key question following the Erin Patterson guilty verdict: what drove her to commit meticulously planned murders?

Host Michael Usher said: "Erin Patterson's story is one of deception, manipulation and, ultimately, murder.

"Now she's been found guilty, we will be using the full weight of our expert panel to investigate how this unassuming mother became one of this country's worst murderers."

The people who knew Erin Patterson best finally speak out, as some of the country's most qualified crime experts break down her motive, her planning and her lies.

Experts joining the live panel include:

· Geoffrey Watson SC, one of the country's top criminal barristers
· Peter Ashkar, forensic psychologist
· Damian Marrett, former detective
· Tita Smith, the 7NEWS reporter who's been following the story since it broke

Plus, the detective behind the world's only other known mushroom murder case shares his insights into the rare and sinister method of poisoning.

Don't miss this remarkable 7NEWS Spotlight special, a forensic deep dive into the mind of a killer, the evidence that sealed her fate, and the haunting question that still lingers: why?