A Brazilian court sentenced Mario Marcelo Santoro to 27 years in jail after he confessed to murdering Cecilia Haddad in 2018 and dumping her body in Sydney's Lane Cove River.
Santoro stood trial and will serve his sentence in Brazil after fleeing to his home country shortly after killing Ms Haddad 13,500 kilometres away.
Associate Professor Tyrone Kirchengast from Sydney Law School described the case as "unusual" and could recall no other examples where an accused stood trial overseas for a murder committed in Australia.
"All states exercise extra-territoriality with the application of their laws and they may do in rare circumstances," Dr Kirchengast told AAP on Friday.
"But they will do so generally where there is inadequate police investigation or prosecution in the country of origin where the conduct occurred.
"Obviously homicide is policed and taken very seriously here in Australia - our laws in that regard are adequate - normally we would be seeking extradition."
NSW detective John Edwards travelled to Rio de Janeiro to assist in providing evidence for the trial and welcomed the result.
"I know I speak for the many police that were involved for a long time in this investigation and it's fantastic to get a conviction," he told the Nine Network.
"It wasn't without challenges with working in foreign languages, I think the result speaks for itself."
Dr Kirchengast who has studied Brazil's legal system said there may be concerns around the length of Santoro's prison term, with the country less inclined to administer long-term prison sentences than in Australia.
"Their attitude towards imprisonment is a bit like the Scandinavian approach - it's very much 'last resort' and generally speaking, prison terms aren't as long," he said.
"It may not be the case that he spends 27 years in prison, so that could be of concern to NSW police and prosecutors as well.
"It's a parole issue and something we may not find out about, maybe through the media in years to come, if he is paroled early."
Santoro broke down as he told the court he and Ms Haddad got into a fight at her Sydney apartment and he "grabbed her neck" and "squeezed really hard".
Testimonies provided by Haddad's family and friends showed the businesswoman had earlier broken up with Santoro but he refused to accept her decision.
Now in his mid-40s, the engineer was convicted of aggravated homicide, asphyxiation, femicide and concealment of a corpse.
Prior to the ruling, Haddad's mother told reporters Santoro was "not a human being but a monster".
On Thursday morning local time in Rio De Janeiro, a jury of six women and one man delivered its decision, which under Brazilian law is still required despite the confession.
Santoro's lawyer said he would appeal the finding.
NSW Police and NSW Police Minister Yasmin Catley declined to comment when approached by AAP.
With AP
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