The suspected killer of Cecilia Haddad has appeared in court for a pretrial hearing in Rio de Janeiro, where an investigator testified that the accused had confessed during informal talks with police while in custody.

Mario Marcelo Santoro was arrested for the murder of Cecilia Haddad on 7 July in Rio de Janeiro, after Haddad’s body was found in the Lane Cove River in Sydney. Both Santoro and Haddad are from Brazil but were living in Australia.

Santoro appeared in handcuffs before the court and remained for the first testimony before being dismissed.

Mario Marcelo Santoro, who was arrested for the murder of Cecilia Haddad. Photograph: Facebook

Fabio Cardoso, the deputy director of Rio’s homicide department said: “In an informal conversation, he confirmed the entire dynamic of the homicide.”

The police officer’s testimony said Santoro admitted to having an argument with Haddad and strangling her to death. He then left the house and returned about two hours later returned and disposed of her body in Lane Cove River.

The testimony added that Santoro said he was telling this story “informally” and that he would only give his formal testimony with lawyers present. However, when Santoro did have legal representation, he refused to answer questions.

The court heard from family members who described Haddad as a happy, hard-working young woman, who loved ballet and scuba diving and was a successful corporate executive. They said she had fallen into an emotionally abusive relationship and was fearful of Santoro, who refused to leave her home and stalked her in public.

The victim’s father, José Haddad, said he spoke by phone with Cecilia Haddad the day before the murder, after she had spent a few days away from her home. Afraid Santoro would be there, she kept her father on the line while she opened the door.

“She told me: ‘Dad, he’s not here, you can go to bed now,’” José Haddad said, holding back tears.

Cecilia Haddad’s stepmother, Andrea Haddad, also testified, saying that the victim had been long suffering “psychological violence,” and that she recalled her calling her crying uncontrollably saying: “I can’t live like this anymore.”

The victim’s brother, João Haddad, gave the fourth and final testimony of the day. He described Santoro as threatening and chauvinistic and said his sister lived in fear of him. He said he saw red flags in Santoro’s obsessive behaviour monitoring Cecilia Haddad’s communication, oftentimes taking her phone and computer.

João Haddad said his sister had blocked Santoro on all communication methods and only exchanged emails with him. She began to only write to him in English purposefully to leave evidence that Australian authorities could quickly understand.

In his testimony, João Haddad recounted several times asking his sister why she didn’t just make him leave or call the police, to which she responded that she was both afraid and also felt bad because Santoro was unemployed at the time.

When João Haddad found out that Cecilia Haddad was missing, he said he called Santoro’s mother, who said her son was not in Brazil. But just five minute later, Santoro called João Haddad saying that he was indeed in Brazil. He then received another phone call from Santoro’s mother saying Santoro was in Brazil and that she was taking a medication and had been confused.

“I could hear [Santoro’s] voice in the background telling her what to say,” João Haddad said.

At least two other witnesses will testify in the pre-trial hearing, including Cecilia Haddad’s mother and her ex-husband. No date has been set for Santoro’s trial. If convicted, Santoro may face up to 30 years in one of Brazil’s notoriously violent prisons.

Kayakers discovered Haddad’s fully clothed body near Woolwich in Sydney on 29 April, about the same time her former live-in lover, Santoro, flew home to Rio de Janeiro.

View of the courtroom before the start of a pretrial hearing of Mario Marcelo Ferreira dos Santos Santoro, in Rio de Janeiro, Brazil. Photograph: Silvia Izquierdo/AP

Investigators confirmed in May that Haddad had asked Santoro to move out of her Ryde apartment, in Sydney’s north-west, in the weeks before her death.

The Brazilian-born Haddad arrived in Australia more than a decade ago and had moved to Sydney in 2016 where she worked for a mining and logistics company in Western Australia.

She had moved to New South Wales to work as a logistics manager for a freight company.