NSW Homicide squad detectives are travelling to Brazil to assist the prosecution over the murder of Cecilia Haddad, following accusations they had withheld evidence.
The body of Ms Haddad, 38, was found by kayakers in the Lane Cove River in Sydney's north in April.
Police in Rio de Janeiro arrested Ms Haddad's former boyfriend, Mario Marcelo Santoro, 40, over the murder in July.
Santoro has been facing a series of pre-trial hearing to determine whether there is enough evidence to proceed to a full trial.
Detective Inspector Wayne Walpole from the NSW Homicide Squad and one other detective left Sydney for Brazil on Sunday with more than 3,000 pages of evidence from their investigation into the Brazilian national's murder.
He said NSW Police assistance was being offered as part of a "complex" process required to ensure evidence gathered in Australia could be considered admissible in a Brazilian court.
It had required sign-off from Commonwealth Attorney-General Christian Porter and his Brazilian counterpart, which had only come through eight days ago, he said.
Detective Inspector Walpole described criticism that Australian authorities had not provided evidence quickly enough as "a misunderstanding of the process".
"It's not a matter of picking up the phone and saying, 'Can you send us half a dozen statements?' It's a matter of going through diplomatic channels," he said.
"We cannot just send evidence over to another jurisdiction … the earliest we could have travelled [to Brazil] is now."
Detective Inspector Walpole said they would be meeting with Australian embassy officials in Brazil's capital before meeting with the prosecutor and homicide squad in Rio.
More than 300 statements have been taken by Strike Force Bronwyn detectives, along with a large number of exhibits and CCTV footage.
"So that will be a matter for the Brazilian authorities to go through what we've got and decide what they need," Detective Inspector Walpole said.
The Australian detectives will also conduct their own inquiries while in Brazil to assist in the NSW Coronial investigation.
