Not long after we first met, the man said that if Australia was looking for Chinese spies, he was just the type of person they would be looking at — but the authorities would never “dare say I’m Chinese intelligence.”

Given the anti-China fervor in Australia, he acknowledged he could come off as suspicious. So why would he not get into trouble with the authorities? He believed that it would be embarrassing for Australia to accuse of him of spying because he had been an active member of a major political party.

His confidence was absolute, and utterly misplaced. Less than two years later, in 2020, he became the first person to be charged under Australia’s broad foreign interference laws. He was accused of acting on behalf of Beijing.

Who was the suspect?

Di Sanh “Sunny” Duong, 68, was born and raised in Vietnam. He was among the hundreds of thousands of ethnic Chinese who fled that country in the 1970s. He settled in Australia and grew a business making tombstones, secured a middle-class life and got enmeshed in local Chinese community groups.

I first interviewed him in 2019 and quickly realized that Mr. Duong was prone to boasting — about his travels, about his family and about his status in society, so much so that it was difficult to take him seriously.

What did he do?

The case against Mr. Duong was not about what he did, but what he was planning to do. Mr. Duong had ties with the Chinese Communist Party, prosecutors said. He had invited an Australian government minister to a charity event, they added, with the intention of someday trying to influence him on behalf of Beijing.

During the trial, the jury was presented with two versions of Mr. Duong: Was he a savvy operator pushing China’s agenda in Australia, as the prosecution would have it, or was he, as the defense claimed, a bombastic braggart?

What was the verdict?

Mr. Duong did not testify in court. But while the trial was underway, he met me, at a pub a stone’s throw from the courthouse, to share his story.

He gave outlandish and convoluted reasons for the actions that prosecutors built their case around. One head-spinning episode involved how Mr. Duong thought he was interacting with a Chinese intelligence officer but later concluded, thanks to a TV show, that the official was not a spy. One thing was clear: Mr. Duong remained adamant that he never did anything against Australian interests.

The jury disagreed. In December, he was found guilty of preparing for or planning an act of foreign interference. Late last month, a judge sentenced him to two years and nine months in prison. Mr. Duong is expected to serve a year behind bars.