Just as his five-week murder trial was due to commence, Borce Ristevski has pleaded guilty to the manslaughter of his wife Karen Ristevski.

New Zealand woman Karen went missing in the early hours of June 29, 2016 and her decomposed body was discovered in bushland at Mount Macedon Regional Park eight months later.

Ristevski had maintained his innocence, insisting his 47-year-old wife had left their Avondale Heights home on foot after an argument.

Police had alleged the Melbourne father of two, 54, killed Karen and driven her body in her black Mercedes-Benz Roadster to dump it.

Ristevski told police he only drove the car to get petrol, changing his mind when the faulty fuel gauge showed it wasn't needed.

He claimed he kept driving towards his wife's dress store Bella Bleu but missed the turn-off so decided to return home.

But detectives allege he lied about his movements that day to avoid detection.

In a hearing last year, a forensic pathologist described the injuries sustained by Karen.

Professor Stephen Cordner told the court she had an irregular break in her hyoid bone — a bone in the neck — that could have been the result of a number of things, including blunt force trauma.

He said it was difficult to say exactly what happened to Karen because her body was found so long after her disappearance.

Ahead of the trial, prosecutors had compiled a 22,000-page evidence brief, including CCTV footage of what they alleged was Mr Ristevski driving his wife's car to dump the body.

A computer systems and digital imagery expert testified at a committal hearing last year that the CCTV footage taken near Diggers Rest shows a car like Ms Ristevski's.

The footage was blurry but Dr Matthew Sorell, a lecturer in telecommunications and multimedia engineering at the University of Adelaide, said the driver in question had features "broadly consistent" with Borce Ristevski.

"I would note the short hair, coloured light grey," he said.

On Wednesday, the day before his Supreme Court murder trial was due to commence, Ristevski dramatically confessed and pleaded guilty to manslaughter.