According to News Corp, Mario Marcelo Santoro gave himself up without resistance on Saturday and simply told officers: “I’ve ended my life”.
The Rio de Janeiro police department said the 40-year-old was arrested at a relative’s home in the city’s Botafogo district over the death of Ms Haddad whose body was found in the Lane Cove River in April.
Local footage shows Santoro being led through a frenzied media pack on his way into a police station.
He was arrested a day after police searched his home in Rio as well as the homes of his parents and relatives, after a warrant for his arrest was issued on Thursday.
A spokesperson from the federal Attorney-General’s office on Sunday was unable to say whether Santoro’s extradition to Australia was being sought.
BREAKING: Mario Marcelo Santoro has been arrested by Brazilian police over the murder of Cecilia Haddad @7NewsSydney
— Ashlea Brown (@AshleaBrown7) July 7, 2018