Sending an ex-teacher convicted of child sexual offences to New Zealand to face similar criminal charges would be unfair and oppressive, his lawyer has argued.
David Peter Kisun, 77, was found guilty of four counts of indecent assault in the ACT Supreme Court in November 2018.
He was handed a 28-month suspended sentence and put on a good behaviour bond for his conduct against two students at Marist College in Canberra in the 1980s.
Kisun, who retired as a teacher in 2014, is fighting extradition to New Zealand over allegations he committed sexual offences against two students at a Marist Brothers school in Wellington from 1969 to 1971.
A NSW magistrate in November signed a warrant surrendering Kisun to New Zealand and sending the convicted child sex offender into custody awaiting his departure from Australia.
The 77-year-old failed in getting bail in December before bringing his challenge to the extradition orders to a head at a Federal Court hearing on Thursday.
Kisun's lawyer Greg Walsh argued his client was mentally unfit to stand trial in New Zealand.
"The evidence is overwhelming that this man has a very significant cognitive decline consistent with suffering from dementia," he told Justice Nye Perram.
Kisun had not been diagnosed with the condition despite "extraordinary efforts", including several attempts to get an MRI scan or an appointment with a neurologist that had been thwarted because he was in custody, Mr Walsh said.
The former teacher's mental state plus a delay of over 50 years in bringing the charges also meant he was no longer able to properly defend himself, his lawyer said.
Mr Walsh submitted that the New Zealand criminal process operated at a lower standard than that of NSW.
In particular, he said those mentally unfit to stand trial in New Zealand would go through a special hearing, where the standard of proof was the balance of probabilities rather than the higher bar of beyond reasonable doubt.
Mr Walsh also argued Kisun could not be extradited because he potentially faced "representative charges" in New Zealand.
When an alleged victim says they were sexually assaulted many times over a period of time but is unable to say exactly when that happened, prosecutors can elect to pursue one charge representing the wider conduct in court.
Mr Walsh said these types of charges were permitted in New Zealand but not in NSW and a court should not agree to the extradition as a result.
Thomas Muir, representing the New Zealand government, supported the extradition, saying there would be no injustice for Kisun.
While there was evidence the elderly man had a "mild cognitive impairment", there was nothing to prove he had been diagnosed with dementia, the barrister said.
Justice Perram said it was troubling that there was a suggestion Kisun had mental difficulties, but he was being asked to make a decision without the proper information in a "glass darkly" approach.
"The consequences to (Kisun) of me getting it wrong are quite significant," he said.
The judge will deliver his decision at a later date.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
