By Alasdair Pal

SYDNEY (Reuters) -An Australian woman accused of murder engaged in a calculated deception to kill three elderly relatives of her estranged husband with a meal she allegedly laced with toxic mushrooms, a court heard on Monday, as closing arguments in the trial began. 

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 them 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 calling the deaths a "terrible accident".

Prosecution barrister Nanette Rogers began her closing arguments on Monday, alleging the accused employed four major deceptions in order to murder her guests.

Patterson first fabricated a cancer diagnosis to lure the guests to the lunch, then poisoned their meals while serving herself an untainted portion, Rogers alleged.

The accused then lied that she was also sick from the food to avoid suspicion, before finally embarking on a cover-up when police began investigating the deaths, the prosecution said. 

"The sinister deception was to use a nourishing meal as the vehicle to deliver the deadly poison," Rogers told the court.

Patterson spent eight days in the witness box after deciding to testify in her defence, including five days of cross-examination. 

She was the only defence witness after the prosecution spent a month calling dozens of witnesses, including estranged husband Simon Patterson and sole surviving lunch guest Ian Wilkinson.  

The court will hear closing arguments from the defence, before the jury receives instructions from presiding judge Justice Christopher Beale and retires to consider a verdict.  

The trial, now in its eighth week and expected to end this month, continues.

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