Lead investigator Paulo Alberes told The Associated Press on Thursday that police concluded Gatti killed himself on July 11 in a seaside resort in northeastern Brazil.
A day after Gatti was found dead, police said they thought his 23-year-old Brazilian wife, Amanda Rodrigues, had strangled him with her purse strap while he slept.
But police began to back off after a coroner's report said that Gatti may have killed himself.
Photos: Murdered Boxing Champ Remembered
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State court judge Ildete Verissimo de Lima in the city of Recife ordered that Rodrigues be immediately released. Her lawyer, Celio Avelino, said Rodrigues would walk out of jail Thursday afternoon.
Gatti was found dead in the apartment he was renting with Rodrigues in the seaside resort of Porto de Galinhas in Brazil's northeast.
The pair, who had a tumultuous marriage, had arrived there a few days before Gatti's death for a second honeymoon. The couple brought their 10-month-old son, who was unhurt and is in the care of Rodrigues' family in Brazil.
PREVIOUSLY ON CRIMESIDER
July 15, 2009 - Arturo Gatti's Dancer Wife Wants Out, Says Attorney
July 13, 2009 - Boxing Champ Murdered by Stripper Wife, Say Police