Robert Kwan, 77, was refused bail in the NSW Supreme Court on Friday on charges relating to three alleged sexual assaults committed across the state decades ago.
Kwan is accused of being the same perpetrator behind an assault on an 11-year-old girl in western Sydney in 1991, a 16-year-old girl in Wollongong in 1996 and a 26-year-old woman in Dubbo in 2002.
Police allege they were able to connect Kwan to all three offences using a DNA matching technique never before used in Australia, known as Forensic Investigative Genetic Genealogy.
It allows police to compare DNA profiles from multiple crimes to match genetic profiles and rose to prominence after it was used in 2018 to identify the "Golden State Killer", Joseph DeAngelo, for a string of murders and rapes in California in the 1970s and 1980s.
Thousands of DNA markers are analysed to identify familial relationships, even as distant as third or fourth cousins, allowing police to identify possible suspects in seemingly unrelated crimes.
Genetic markers are compared against two publicly available genealogy databases which allow police access to the profiles of people who consent to their information being used in solving serious crimes.
Justice Helen Roberts said one of the factors in her decision to deny bail was the seemingly extremely strong DNA evidence relied on by the prosecution coupled with other circumstantial details to identify Kwan.
However, Kwan's barrister Sharyn Hall SC raised potential doubts over the validity of the evidence given the technique has never yet been tested in an Australian court.
"We don't how (police) made the link to Mr Kwan," she said.
"The biggest issue in this case will be the uniqueness of the DNA argument ... we don't have any of that DNA material at this stage."
Ms Hall said she could not accurately assess the strength of the argument put forward using the genealogy technique without the evidence being provided.
But Justice Roberts said the extremely serious nature of the alleged offending, which involved allegedly assaulting all three women in his car, meant he was an unacceptable risk.
Kwan's case will next be heard in Wollongong Local Court on July 22.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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