Paul Holmes and his sister Maree were bracing themselves to face the details of how their brother, mother and stepfather had been murdered.

But as the jury was being empanelled, the accused killer Ian Francis Jamieson had a sudden change of heart.

After 18 months of denials, he pleaded guilty to the triple murder, which arose from a neighbourly dispute over dust from a dirt track in rural Victoria.

Jamieson, 65, admitted murdering his neighbour Greg Holmes, 48, and Holmes' elderly mother and stepfather Mary and Peter Lockhart near Wedderburn in October 2014.

Ian Jamieson has pleaded guilty to murdering 3 people at their Wedderburn property. Trial was due to start today pic.twitter.com/2VzGD87a3c — Emily Angwin (@EmilyCAngwin) April 5, 2016

Jamieson's 11th-hour change of heart shocked the family.

"I think he's finally stood up for what he's done," Paul Holmes told reporters outside the Victorian Supreme Court in Bendigo.

"We're very relieved - there was a bit of trepidation about what we were going to see and hear."

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Greg Holmes had two children when he was tragically killed. Photo: 7 News

On October 22, 2014, police responding to a dispute between two neighbours found Mr Holmes' body in a paddock near his home.

The officers then heard gunshots across the road.

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Mr Lockhart. Photo: 7 News

They retreated and cordoned off the area before a lengthy negotiation ended with the gunman's surrender.

The bodies of 75-year-old Ms Lockhart, and her husband, 78, were later found in separate locations on their property.

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