A 53-year-old professor at the Chinese University of Hong Kong (CUHK) was sentenced to life in prison on Wednesday after being found guilty in the High Court of murdering his wife with a gas-filled yoga ball.

A jury of five men and four women unanimously found that Malaysian Khaw Kim-sun killed his wife Wong Siew-fing, 47, and their daughter Lily Khaw, 16, by gassing them after leaving a yoga ball filled with carbon monoxide inside his wife’s car in May 2015, the Oriental Daily reported.

Justice Judianna Barnes said it was shocking that such a clever and successful man could use such a calculated method to kill his wife and daughter.

The mother and daughter were found by a passer-by in the Mini Copper parked on a roadside near their home in Ma On Shan, the New Territories, and later died in a hospital. A deflated yoga ball was found in the boot of the vehicle.

The doctor at the Prince of Wales Hospital in Sha Tin and associate professor in anesthesiology at the CUHK was seen by colleagues filling two yoga balls with carbon monoxide.

Khaw claimed he obtained the poisonous gas for experiments on rabbits at the school and later took the gas home to kill rats with it. His defense team argued that either Wong or Lily Khaw could have placed the gas-filled yoga ball in the car and removed the stopper in order to commit suicide.

However, the jury did not believe this story.

The court earlier heard that the defendant discussed divorce with his wife in 2013 after his wife discovered he was having an affair with his research assistant. But the pair did not get divorced and stuck together only to raise their children, the court heard.

After the sentence was passed, Khaw reportedly turned to look at his three other children, who were also in court to hear the verdict, shaking his head as if to say he did not do it despite the court decision, according to Apple Daily.

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Read: Professor denies killing wife and daughter with gas-filled yoga ball