Edmund Ian Riggs, 60, was on Wednesday found guilty of the manslaughter of his wife of 17 years, Patricia Anne Riggs, in September 2001 at their home in Redcliffe, north of Brisbane.

Riggs was acquitted of the more serious charge of murdering his wife.

The Brisbane Supreme Court jury accepted Riggs' testimony that Mrs Riggs died after he pushed her in reaction to her spitting on him as they fought at their home.

She hit her head on the bed and he panicked when he realised she was dead. Sentencing is expected in two weeks.

Trish's brother Mark Knowles, of Conder in the ACT, was in the court in Brisbane to hear the verdict, along with many other of Mrs Riggs' family, including some from Queanbeyan and Cooma.

"We're disappointed with the outcome but the jury has come to that decision,'' Mr Knowles said.

"Unfortunately, because of the time that has passed, obviously, that's the result we get.

"It was one of those things where he got to have his say in court and Tricia didn't.''

Mr Knowles said as difficult as it was, the family wanted to be in court.

"We as a group needed to show we loved Trish and she will never be forgotten,'' he said.

A former swimming instructor and home birth advocate originally from Canberra, Mrs Riggs – Trish or Tricia to her friends and family – was listed as missing for nearly 15 years before her remains were found in the backyard of her Queensland home in 2016.

Riggs secretly buried her in a shallow grave on the outskirts of Caboolture and pretended she had abandoned him and their children.

He dug her remains up a few years later after seeing heavy machinery at the site, in fear she would be found.

He reburied her at the family home, where her partial skeletal remains were found in 2016 by a new owner who was concreting behind a shed.

The entirety of her remains have not been found.

Riggs lied about her whereabouts for nearly two decades, including to their four children, saying he believed she had run off on them.

The lie continued until his trial last week when he pleaded guilty to misconduct with a corpse.

Mrs Riggs, a mother-of-four, was living in Canberra as late as January 2001 when she worked at the Olympic pool. She had attended  Griffith Primary, Telopea Park School and Narrabundah College and married Riggs when she was just 17.

The family moved to Brisbane in August of 2001.

Mrs Riggs, then 34, was last seen at her home in Margate in the early evening of September 30, 2001 and was reported missing to police three days later, on October 3.  Police were told then she had walked out of her Brisbane home after an argument with her husband.

Her mother Carol Saxton, of Queanbeyan, fought for years to discover the truth behind her daughter's disappearance.

Mrs Saxton died in September, 2011, never finding the answer.

"She worked so hard to get to the truth and he had so many opportunities to tell the truth,'' Mr Knowles said, on Wednesday.

The ashes of Mrs Riggs' partial remains were interred at the Queanbeyan Lawns Cemetery in October, 2016. She was laid to rest next to her mother.

Mr Knowles said the family now wanted to find the rest of Mrs Riggs' remains.

"We only got partial remains recovered,'' he said. "They've got a law in Queensland called 'no body, no parole' and we've asked Queensland police if they can, through that, pursue Patricia's remains so that we can get some closure. And we can bury her all in the one spot, next to her mother.''

During the court case, Mr Knowles said none of Mrs Riggs' four children wanted to interact with her side of the family. They supported their father, he believed.

"We didn't lose one member of the family we lost five because of his lies. That's the real unfortunate tragedy out of all this,'' he said.

In court, Riggs laid bare his troubled marriage.

He and Mrs Riggs fought over his failure to financially contribute to the family due to a work injury.

On the night she died on September 30, 2001, Riggs said Patricia laughed at him when he claimed he wanted to make peace.

Riggs said his wife told him she'd found a list of escorts in a pocket of his shorts.

Then she revealed she'd had numerous affairs with men she had met through swim coaching and at nightclubs.

He said when he realised Patricia was dead, his brain "exploded" .

Fear that their four kids would be "orphans" if he was jailed prompted him to cover up the death, he said.