When police showed Bourke a copy of an anonymous threat sent to Councillor Jacqui Rudge's home in March 2020 telling her to step down or her history of mental illness would be revealed, he read the document intently.
"I know a letter that was sent to Councillor Rudge but I didn't know about this one," Bourke told detectives during a recorded interview.
Prosecutors told Bourke's trial this was a telling clue the 67-year-old knew about the threat to Mrs Rudge - how could he otherwise tell the difference between one letter and another?
After five hours and 15 minutes of deliberations, a NSW District Court jury in Orange found Bourke guilty of misconduct in public office on Wednesday.
The jury accepted the crown case that Bourke and his longtime friend and campaign manager Darryl Leahey were part of a joint criminal enterprise to blackmail Mrs Rudge.
The unsigned letter "recommended" she stand down from her position on council within seven days or her history of mental illness would be aired publicly.
Crown prosecutor Paul Kerr described the letter as a "blunt instrument" against Mrs Rudge.
She had run on Bourke's election ticket but sometimes voted against him, including over a $2.5 million loan for a go-kart track on Mount Panorama.
"He was supposed to be a leader," Mr Kerr told the jury in his closing address.
"Instead he engaged in conduct designed to undermine the democratic system of local government."
The law of misconduct in public office is not often applied.
Outside of the presence of the jury, the cases of disgraced former NSW Labor figures Eddie Obeid and Ian Macdonald loomed large in legal argument.
Bourke's slip-up with police was one of several pieces of evidence that firmed up the circumstantial case against him.
The former mayor long maintained Leahey typed out the letter but Bourke said he was unaware of its contents.
Bourke admitted he arranged for a volunteer at the community op-shop he ran to buy an envelope, then asked another worker to address it to Mrs Rudge and send it.
One of the volunteers described buying the envelope and being directed by Bourke to drop it on the floor of his car.
Leahey admitted to a local journalist he was the author of the note in October 2021 and he was later charged and convicted in the local court.
Eight character witnesses, including former Orange mayor Reg Kidd, described Bourke as a compassionate man, who cared deeply for disadvantaged people.
Mr Kerr said the Crown was not suggesting Bourke was an "uncaring monster".
"He lost his moral compass when he agreed with Darryl Leahey ... to send a letter to Jacqueline Rudge threatening to reveal her mental health issues."
Bourke was motionless as the verdict was handed down and he did not comment outside court.
Judge Penny Musgrave set a sentencing hearing for September.
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