The man accused of killing businesswoman Cecilia Haddad is in custody in Brazil, with Australian police set to fly to the South American country to assist local officers.
Mario Marcelo Santoro was arrested in Rio de Janiero on Saturday (Sunday AEST) over the death of his former girlfriend Ms Haddad, whose fully-clothed body was found in Sydney's Lane Cover River in late April.
Detectives reportedly found Santoro, 40, at his sister's apartment in the Botafogo district of Rio.
Local footage shows Santoro, who flew back to his native Brazil about the time of the murder, being led through a frenzied media pack on his way into a police station.
NSW homicide detectives were on Sunday night ready to travel to Brazil but were still awaiting "international protocols" to be met.
"NSW Police Force is continuing to work through Commonwealth processes in order to bring a successful conclusion to their investigation," a spokeswoman told AAP.
NSW Police issued a warrant for the 40-year-old's arrest last month but Santoro may never face charges in Australia because it's unconstitutional for Brazil to extradite its citizens.
Santoro's arrest was marked by Haddad's friends, including South American actress Dani Suzuki.
"Here or in another world, all your actions will have consequences and all justice will be done," Suzuki posted to Instagram.
"Justice starts now," another friend posted to Facebook.
Fabio Cardoso, from Rio's homicide division, said police believe Ms Haddad, a Brazilian mining executive, was killed by asphyxiation after "not accepting" a break-up.
"We know he had the key to her house because he lived there for a while," Mr Cardoso told the Seven Network in Brazil.
The federal attorney general's office on Sunday wouldn't comment on whether Australia was seeking Santoro's extradition.
Foreign Minister Julie Bishop last week told reporters Australian authorities were "working closely" with their Brazilian counterparts to ensure an "appropriate" outcome.
