Foreign spies would gain a wealth of information if details of some secret trials relating to national security breaches were made more public, Australia's domestic spy agency has warned.
The Independent National Security Legislation Monitor heard from a range of experts at a Wednesday public hearing over whether national security laws allowing a former intelligence officer, known as Witness J or "Alan Johns", to have his case heard in total secrecy were appropriate.
Australian Security and Intelligence Organisation director-general Mike Burgess said his agency supported being more open and transparent but cautioned there was a limit to that commitment.
"This is a security issue as well as a safety issue," Mr Burgess said on Wednesday.
"Foreign intelligence services are seeking to obtain classified and privileged information to gain advantage over Australia's defence."
He later added even disclosing a closed court hearing's location could help foreign spies piece together clues to confirm the identity of national intelligence officers.
"They also look for innocuous information they can use to piece together to unravel or reveal more sensitive information, including about our sources, methods and capabilities," Mr Burgess said.
"For reasons I've explained, it is important that options continue to be made available to protect highly sensitive information in criminal proceedings."
Office of National Intelligence first assistant director-general Kathryn McMullan also warned "determined adversaries" would target criminal proceedings dealing with matters of national security if laws were relaxed.
"Ultimately, decisions about the public disclosure of intelligence information require complex and careful considerations about the possible harm that could occur from any disclosures on a case by case basis," Ms McMullan said.
Both Mr Burgess and Ms McMullan stressed the importance of maintaining trusted intelligence sharing with international security agencies, which added another challenge if certain information revealed in trials was not concealed.
Legal and human rights experts earlier offered potential solutions to strike the balance between allowing for transparent and open judicial hearings while containing risks to national security.
Human Rights Law Centre senior lawyer Kieran Pender said similar examples in countries such as the United Kingdom showed both camps could be appeased with adjustments to the laws.
He offered three key recommendations - the court should be made to provide reasons for why a case is to be closed to the public, a "secret judgments library" should be established and periodically reviewed to determine whether secrecy is to be maintained, and a new scheme to argue a public interest case in open justice should be created.
"The balance between national security concerns and open justice can be struck in a manner that accommodates both without reducing open justice to nothing," Mr Pender said in his opening remark.
National security legislation monitor head Grant Donaldson said he was considering launching further inquiries into the use of national security laws in the cases of Bernard Collaery and Witness K.
"I will be considering that matter at the appropriate time," Mr Donaldson said in a March hearing.
"There has been a great deal of disquiet concerning the invocation of the NSI Act in the circumstances of the Collaery matter."
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