A lawyer for William Tyrrell's former foster mother has accused police of a campaign to ambush her after she was secretly recorded kicking and threatening to slap another child.
The 58-year-old woman appeared alongside her 56-year-old partner in Parramatta Local Court as both faced allegations of assaulting and intimidating the child, who was in their care before being removed in November 2021.
But her barrister, John Stratton SC, questioned why police had sat on the domestic violence allegations until that month, which coincided with her being called before the NSW Crime Commission over William's unsolved disappearance.
"Your purpose in doing that was so an ambush could be sprung on (her)," Mr Stratton told the officer in charge of the investigation, Detective Senior Constable Sean Oglivy.
"I wouldn't use the term ambush," the detective replied.
He denied the suggestion the domestic violence-related charges had anything to do with putting pressure on the foster mother to "break her".
In a clash covertly recorded by police in October 2021 and played to the court, a loud bang could be heard followed by the youngster screaming in pain.
"She kicked me," the child was heard yelling.
"You're a bad mother."
The child, who is not William, later said they did not wish to stay with the couple, leading to the mother ranting about the youngster having a "get-out-of-jail-free card".
"You break our hearts, you lose the only parents you've ever known, the only parents who have fought tooth and nail for you," the foster mother was heard saying.
In a later conversation with another woman, the foster mother said she had "lost it" as she kicked the child.
"I don't have words to describe how I feel on the back end of doing that," she said.
Chatting with William's former foster father, the woman said she kicked the child hard during a "crisis point" for the family, pointing out the ongoing investigation into the young boy's unsolved 2014 disappearance.
"We've got this investigation hanging over our head," she said.
"We've got police looking at me … how do I live with that? Being looked at."
The woman said in another call on the same day that police had focused on her because they had no other suspects in William's case.
"They're doing it because they f***ed it up," she said.
"They've cleared the guy who should still be a suspect."
After the call, she apologised to the child for being "completely out of line" with the kick.
"So I am sorry that I lost control and I'm sorry that I did that."
In May 2021, an argument was recorded in which the foster mother accused the child of throwing things around the home.
"If I see or hear you throw something around again that won't be the only thing that gets thrown," the woman said.
"You seem to only listen to me when I threaten to get violent with you."
A July argument over packing the dishwasher led to the foster mother threatening to pack up the child's things in a black plastic garbage bag.
"If I get that attitude ... I'm going to slap you across the face," the woman said.
She has pleaded guilty to assaulting the child by hitting her with a wooden spoon in January 2021 and kicking her in October but is fighting two intimidation charges over incidents between January and August that same year.
Her partner has pleaded not guilty assaulting the child by allegedly grabbing their neck on October 2021 and intimidation in November 2020.
Neither foster parent can be named for legal reasons.
The covert recordings from inside the foster parents' house on Sydney's north shore, their car and the couple's telephone conversations were made during a police investigation into William's disappearance.
The hearing continues.
William was three years old when he vanished from a Kendall property belonging to his foster grandmother on the NSW mid-north coast.
No one has been charged over his disappearance.
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