Daniel Duggan, 55, has spent 17 months in a maximum-security prison as he fights a US extradition order.
He was arrested in Australia at the behest of the US after being accused of breaching American arms trafficking laws by providing military training to Chinese pilots in South Africa between 2010 and 2012.
Former US military pilot Daniel Duggan says spy charges against him are politically motivated. (HANDOUT/DUGGAN FAMILY)
He received about $100,000 for his services, US lawyers said as they were successful in a bid to freeze the sale of his house after they argued the cash was illegally gained and could be frozen.
The former US top gun stands accused of training the Chinese military to land on aircraft carriers. He renounced his US citizenship in 2012 and became an Australian citizen in the same year.
Duggan and his family argue the charges are politically motivated given the deterioration of the Sino-American relationship and how long ago the alleged actions occurred.
In a letter from prison, seen by AAP, Duggan said he believed his activities weren't illegal and the Australian Security Intelligence Organisation (ASIO) and the US Naval Central Intelligence Service (NCIS) knew of his work.
"Neither ASIO or NCIS made any claim or gave any warning that the activity was considered illegal," he wrote.
When he offered not to return to South Africa or China to intelligence agents, he said they were "indifferent" about his work and told him they didn't want to interfere with his business in the region.
Saffrine Duggan and her children are fighting for the release of husband and father Daniel. (Dan Himbrechts/AAP PHOTOS)
And it was ASIO agents who brought up being able to meet Chinese generals and the topic of intelligence in a 2012 interview, leading to him believe they were trying to recruit him as a spy, Duggan said.
ASIO said it was unable to comment because the matter was before the court.
Duggan's wife, Saffrine, presented a petition with 25,000 signatures to politicians in Canberra, calling on Attorney-General Mark Dreyfus to release her husband and end his extradition.
"We would like him to exercise his right as attorney-general to step in here and help an Australian citizen," she told AAP.
Mr Dreyfus declined to comment.
Duggan's imprisonment has also impacted his six kids, with Australian Paediatric Society vice president Paul Anthony Bauert expressing serious concerns.
The children exhibited "unmistakeable signs of stress and severe anxiety," Dr Bauert wrote in a separate letter.
"The single important cause in these children's deteriorating health is the separation from and uncertainty for their father's future."
Duggan's case returns to court in Sydney on Friday.
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