By Alasdair Pal

SYDNEY (Reuters) -An Australian woman accused of murdering three elderly relatives of her estranged husband using a meal laced with toxic mushrooms had no motive to kill them, her lawyer told the court on Tuesday as the defence began its closing argument.

Erin Patterson is charged with the murders of her mother-in-law Gail Patterson, father-in-law Donald Patterson and Gail's sister, Heather Wilkinson, along with the attempted murder of Ian Wilkinson, Heather's husband, in July 2023.

The prosecution accuses her of foraging for poisonous death cap mushrooms, drying them and knowingly serving the mushrooms in individual portions of Beef Wellington at her home in Leongatha, a town of about 6,000 people some 135 km (84 miles) from Melbourne.

Patterson denies the charges, which carry a life sentence, with her defence earlier calling the deaths a "terrible accident".

On Tuesday, Patterson's barrister Colin Mandy said prosecution evidence that the accused's relationship with estranged husband Simon Patterson had soured after a disagreement over child support lacked logic. 

"Whatever we might call those spats and disagreements and frustrations, it doesn't provide any kind of motive to murder someone's parents," he told the court. 

In fact, the accused had a good relationship with the Patterson family, he added, saying she had loaned Simon Patterson's siblings hundreds of thousands of dollars to buy property. 

Earlier on Tuesday, barrister Nanette Rogers ended the prosecution's closing argument by accusing Patterson of a calculated trail of deception before and after the lunch.  

"Erin Patterson told so many lies it's hard to keep up with them," Rogers told the court. 

"She's told lies upon lies because she knew the truth would implicate her."

After the defence concludes its closing statement, presiding judge Justice Christopher Beale will give his instructions to the jury before it retires to consider a verdict.

The trial, which is now in its eighth week and has gripped Australia, is expected to conclude later this month.

(Reporting by Alasdair Pal in Sydney; Editing by Kate Mayberry)