An Indonesian domestic worker was summoned to Hong Kong’s High Court on Thursday to testify at the high-profile trial of Chinese University of Hong Kong associate professor Khaw Kim-sun. Khaw is on trial for the murder of his wife and one of his daughters, who died from carbon dioxide poisoning inside a Mini Cooper after the gas leaked from a yoga ball in May 2015.

The helper had been with the Khaw family for some five months prior to the incident. She told the court that the defendant, a father of four who taught at the university’s Department of Anesthesia and Intensive Care, never shared a bed with his wife. She also stated that she did not witness either of the deceased – the 47-year-old wife surnamed Wong and the 16-year-old girl – carrying a yoga ball into their car on the day of the murders.

Police investigators found a deflated yoga ball, whose opening was not securely plugged, in the boot of the car. Post-mortem examinations concluded that the deceased had both died from carbon monoxide poisoning.

It is believed that on the day in question Khaw’s wife was driving the car to pick up her other children, and that the teenage victim only rode with her mother as she did not have school that day.

The helper said Khaw enjoyed sound ties with his four children, but she could not judge the defendant’s relationship with his wife.

Earlier, Khaw admitted during police interrogation that he had filled a yoga ball with carbon monoxide at a university’s laboratory two days before the incident in order to “kill laboratory mice”.

But the prosecutor pointed out during the trial that anyone, let alone an expert on anesthesiology, who put a fitness ball full of deadly gas inside a confined space “would be intent on murder”.

Khaw was having an affair with a university research assistant 20 years his junior and had sought to divorce his wife, according to the Sing Tao Daily.

Reports say divorce discussions foundered on a failure to reach an agreement on child custody and the division of their assets. These included HK$6 million in bank deposits, a three-story villa in Hong Kong’s idyllic Sai Kung district and other properties. Khaw’s wife had reportedly suffered depression and other mental illnesses which were possibly linked to her husband’s extra-marital affair.

It was also revealed in court that, after the deaths of his wife and daughter, Khaw and his girlfriend repeatedly traveled outside Hong Kong, even while the police were still gathering evidence to prosecute him.