An anaesthetist convicted of killing his wife and daughter by placing a yoga ball which leaked carbon monoxide in their car has been sentenced to life in prison in Hong Kong.

Malaysian citizen Khaw Kim Sun, 53, had become estranged from his wife, Wong Siew Fing, 47, and their four children, although they continued to live together while he had an affair with a student.

A jury of five men and four women found him guilty at Hong Kong’s High Court after seven hours of deliberation.

Judge Judianna Barnes Wai-ling told Khaw: “It is shocking that a highly educated and successful man would conjure up such a calculated method to get rid of his wife.”

Khaw was accused of putting the gas-filled yoga ball in the boot of a Mini Cooper driven by his wife, Wong Siew-fung, on May 22 2015.

Ms Wong and their 16-year-old daughter were found unconscious in the car parked at a bus stop about an hour after leaving home. They were later declared dead from severe carbon monoxide poisoning, although the vehicle showed no defects such as a leaky emissions system.

The case initially flummoxed Hong Kong police until the presence of the deflated yoga ball drew suspicion.

Khaw was arrested in September after colleagues from the teaching hospital where he worked spoke with police.

He reportedly obtained the carbon monoxide from the hospital, telling colleagues he wanted to “test its purity” and its effects on rabbits, according to accounts.

Khaw reportedly told police he took the gas home to use it to exterminate rats at home, although a domestic helper employed by the family testified that they had no rodent problem.

While Khaw stood to inherit considerable amounts of property co-owned with Ms Wong following her death, there was no apparent motive for killing his daughter, leading to speculation that her death was unintentional.