The sister of slain Canadian boxing champ Arturo Gatti believes the fighter was locked in a toxic relationship with his 23-year-old wife.

Officers say the 37-year-old boxer was strangled to death after he fell into an alcohol-induced sleep. Gatti was found dead early Saturday morning at a seaside resort in northeastern Brazil.

His wife, Amanda Rodrigues of Brazil, has been taken into custody and formally accused.

According to sister Anna-Maria Gatti, the entire family disapproved of the boxer's two-year-old relationship, and they warned Gatti that the young woman was allegedly out for the fortune he had earned during a 16-year career in the ring.

"We told my brother, my mother told him, 'Leave her.' The only reason he didn't want to leave her was the boy, his son," the sister said.

Rodrigues denies any wrongdoing in the death and says she awoke at 6 a.m. on Saturday to find Gatti dead in the couple's rented room at the Porto de Galinhas resort.

However, police say that Rodrigues has not adequately explained how or why she stayed in the room for 10 hours after Gatti was apparently killed.

None of the allegations have been proven in court.

Investigator Moises Teixeira alleged Monday that Rodrigues likely acted alone in the death, as no one else could have entered the couple's room.

"It was technically impossible for a third person to have been in the flat," Teixeira told The Associated Press.

"The investigation isn't finished, but we continue to think she did this alone."

Meanwhile, Rodrigues' lawyer said his client is too "fragile" to have killed the boxer.

Police are also looking into Rodrigues' claim that the couple had a fight the night before he was found, and that he was drunk and returned to the hotel room alone afterwards.

Tom Phillips, a freelance journalist working in Brazil, said the death has become a major story across the country.

"The local people are very shocked because it's a very chic, sophisticated resort where people go to get away from the city and lie on the beach and spend lots of money on cocktails. It's not the place where you normally get murdered," he told CTV News Channel.

Meanwhile, friends and family of the former junior welterweight champion from Montreal were mourning the sudden, unexpected loss.

Victor Salvatore, a friend of Gatti's from Montreal who has known him since he was a boy, said the boxer's death is an "amazing shock."

"Arturo was a good guy, always happy always willing to help you out, always in a good mood, a good guy, a fun guy who had a 10-month old boy, and he was super happy to be a father. This comes at a really bad time in his life," Salvatore told CTV's Canada AM.

Investigation in progress

According to Pernambuco state police spokesperson Milena Saraiva, the police investigation is not yet complete.

Saraiva told The Associated Press that Gatti was strangled with the strap of a purse, which was found at the scene covered with blood stains. Gatti also had a head injury.

The couple arrived at the resort in northeastern Brazil on Friday with their one-year-old son, Arturo Jr., who is now being looked after by Rodrigues' sister.

Four-time world champion boxer Acelino (Popo) Freitas, who is from Brazil, told Globo TV's website that he was close to the couple and that he "knew they were having some sort of problem and were about to separate."

Gatti was a former junior welterweight champion who compiled a 40-9 record during a 16-year professional career.

Gatti, who was born in Italy but grew up in Montreal, had an all-or-nothing fighting style that often led to bloody punch ups in the ring, making him a fan favourite.

Salvatore described his friend as a "guts and glory, heart and soul" type of fighter who never let his fame or money go to his head.

"He was always happy, always ready to sign an autograph, to take a picture with you, always ready to have a drink with you and just be a normal human being. He hit rock star status but he never thought for one second that he was that popular," Salvatore said.

Gatti retired from professional boxing in 2007. After spending much of his boxing career in the United States, Gatti moved back to Montreal, where he got involved in the real estate business.