Desmond Gore, 73, abused the girl for two years at his Armadale home in Perth before it came to light he had sexually exploited at least six children, five of whom were under his care.
An eight-year-old girl wrote a disturbing note saying she was sad when she had "'sex with her granddad", referring to her foster carer who raped her repeatedly.
73-year-old Desmond Gore was slapped with 20 charges of sexual abuse—including the rape of three eight-year-old girls—after he pleaded guilty to the abuse at Perth District Court on Tuesday, Daily Mail reports.
The abuse took place at Gore's residence in the suburb of Armadale, located in southeast Perth, from 2007 to 2010.
The offense became apparent after a caseworker came across one of the victim's belongings, which included a letter the girl had written. "I feel safe when loved. I feel sad when I have sex with my granddad," she wrote.
This isn't the first time Gore is facing allegations of sexual abuse. Two years prior to the abuse of the girl in question, who was eight at the time, the Department for Child Protection received a different allegation from another child who was under his care.
The first victim was taken away from Gore after she confessed to his wife about how he abused her.
While a caseworker was also in the know, Gore wasn't charged and the Department of Child Protection continued to place children in his care.
It eventually came to light that Gore had abused six children in total, including five who were directly under his care.
It was only after the discovery of the box containing his abused victim's letter that Gore's carer status was suspended and a review into his conduct initiated.
The discovery led to the girl pouring out details to her caseworker of how Gore would rape her when his wife was not home.
After learning of the episode, two more children were encouraged to come forward and reveal details from the abuse the suffered under Gore.
According to the report, one of the abused children was under the couple's care for less than a month.
That said, Gore always denied accusations from all seven complainants and branded their stories "complete and utter lies."
"It's all about the money, nothing else, nothing else," Gore said in court as reported by WA Today.
Gore went a step further and told the jury he had no sexual proclivity towards children.
Furthermore, he said he couldn't have raped them because he was "impotent" during the time of the alleged abuse.
Nevertheless, the jury deliberated for just one day after a week-long trial and found him guilty on 20 of the charges laid against him.
Gore has now had his bail revoked and is scheduled for sentencing on Friday.