The foster mother of William Tyrrell has been found not guilty of lying to the NSW Crime Commission, and has urged police to focus their efforts on looking for the missing boy.
Last year, both foster parents were charged with assault of a child at a home on Sydney's north shore.
The child is not William, who has not been seen since he went missing in 2014, aged three.
It's alleged the 57-year-old foster mother, who cannot be named for legal reasons, hit the child with a wooden spoon.
She was called to give evidence to the Crime Commission in November last year about the disappearance of William Tyrrell.
Police said the foster mother lied in the hearing about the alleged assault, stating she had never hit a child with a wooden spoon, but did admit to hitting and kicking them.
During the trial in Sydney's Downing Centre Local Court this week, it was revealed police obtained warrants to plant multiple listening devices in two locations and had also intercepted the foster parents' phone calls.
Audio from one of those devices was played in court on Thursday allegedly capturing the alleged wooden spoon incident.
The foster mother's barrister, John Stratton SC, argued it could not be proven beyond reasonable doubt his client knowingly lied as she was clearly distressed during the Crime Commission hearing, which was held behind closed doors.
Magistrate Miranda Moody told the court she could not discount the possibility the foster mother was mistaken and not lying when she gave evidence to the crime-fighting body.
"She was clearly, frequently, highly distressed … clearly aghast at the allegation she had anything to do with the disappearance of her foster child [William Tyrrell]," Magistrate Moody said.
The Magistrate said had the foster mother denied hitting and kicking the child "I might have taken a different view".
The Crime Commission works alongside police and can hold hearings and supply evidence to courts to facilitate prosecutions.
Outside court, the foster mother became emotional when she welcomed the "detailed judgement".
"With this behind me, I hope that the police focus on finding William and what happened to him," she said.
On Thursday, a detective involved in the William Tyrrell case told Sydney's Downing Centre Local Court he formed the belief the foster mother knows where the missing boy is.
Under cross-examination Mr Stratton SC put to the detective one of the reasons for laying the charges was to "break [the foster mother's] spirit".
Last year, police engaged in a four-week search around the foster grandmother's house in Kendall, on the Mid-North Coast, where William was last seen.
Officers searched and dug up nearby bushland while using a ground-penetrating radar to investigate underneath the house.
The police investigation into the three-year-old's disappearance is ongoing.
