Australian law doesn't recognise "the criminal offence of traitor", an international law expert says as calls grow to out a former politician who was revealed to have helped a foreign spy ring.
ASIO Director-General Mike Burgess revealed a unit within a foreign spy service had targeted Australia and managed to recruit a former politician who "sold out their country, party and former colleagues to advance the interests of the foreign regime".
The former politician also attempted to introduce a prime minister's family member to the spies but the plot did not go ahead.
The coalition would work with the government to amend the necessary legislation to make foreign interference laws retrospective, Opposition Leader Dutton said.
"The most egregious act is from somebody in public office who betrays their country and I wouldn't have any tolerance for it whatsoever," he told Sydney radio station 2GB.
Despite others having branded the former politician a "traitor", the term didn't translate into a criminal offence, Professor Don Rothwell said.
But there are the crimes of treason and espionage, he said.
With foreign interference laws only coming into place in late 2018, it could be devised that the former politician was active before that time or that authorities didn't have enough evidence to support a prosecution, he said.
"The result is that the conduct of the politician has been revealed in the public domain, but no criminal charges will be laid."
The opposition and former Liberal treasurer Joe Hockey have called for the person to be publicly outed, arguing keeping their identity hidden smeared all politicians and created distrust amongst Australia's allies.
"You can't make an allegation about someone being a traitor and then expect that no one will ask questions," Mr Hockey told Sydney radio 2GB on Thursday.
Mr Dutton said: "If he doesn't indicate the name, then there's a cloud hanging over everybody else".
He said he would "put my money" on a former NSW Labor politician and the country being China but didn't offer any evidence or further details.
Parliamentarians have privately speculated about former politicians from all stripes of politics.
It would be unfair to publicly name someone who wasn't being charged, especially with the risk of defamation, opposition home affairs spokesman James Paterson said.
Government ministers have backed the director-general's decision not to name the person.
Asked why he didn't out the former politician, Mr Burgess said Australia was a rule of law country and the person wasn't active anymore.
But they would be caught if they started doing it again, the director-general said.
"Several individuals should be grateful the espionage and foreign interference laws are not retrospective," Mr Burgess said.
Foreign spies posed as consultants, head hunters, local government officials, academics and researchers and targeted students, academics, politicians, businesspeople, law enforcement officials and public servants, he said.
They offered cash for information, with premiums for insider details.
The ring also flew academics and political figures to another country for an all-expenses-paid trip where they ended up meeting spies disguised as bureaucrats and later wrung information out of them.
Blowing their cover had put the entire operation on notice, Mr Burgess said.
He also expressed frustration at suggestions "convictions are the only weapon in our collective arsenal or the only measure of our success".
Other actions included working with partners to cancel visas, directly confronting spies or their organisations and issuing public rebukes.
Sunlight was the best disinfectant, Home Affairs Minister Clare O'Neil said, while defending the decision to keep Australians in the dark about the person's identity.
Pressed on previous naming and shaming, Ms O'Neil said it was "a question about what's in the national interest at different points in time".
The remarks came just before former Liberal Party candidate Di Sanh Duong, 68, on Thursday became the first man found guilty under Australian foreign interference laws.
He will spend at least 12 months behind bars.
