Hong Kong's Yoga Ball Murder: What to Know

When colleagues caught him filling two yoga balls with carbon monoxide, anesthesiologist Khaw Kim-sun said he wanted to take them home to experiment on rabbits. Then his wife and daughter were found dead in their car, the deflated exercise equipment in the trunk. Autopsies showed they died of gas poisoning.

Khaw, 53, is on trial in Hong Kong on two counts of murder in what prosecutors called a "deliberate and calculated" plot. He has pleaded not guilty.

Prosecutors said Khaw put the gas-filled inflatable ball in the trunk of the car, where it leaked carbon monoxide and killed his wife, Wong Siew-fung, and their 16-year-old daughter on May 22, 2015, according to the South China Morning Post.

Here's what to know about case.

Prosecutors told Hong Kong's High Court Wednesday that the Malaysian-born professor was having an affair with a student and had become estranged from his wife and four children. The family, however, continued to live together as the wife would not agree to a divorce.

Prosecutor Andrew Bruce alleged that Khaw deliberately plotted to kill his wife and, under the guise of a research project, spent thousands of dollars procuring 99% pure carbon monoxide to pump into the yoga balls, which he took home. He was reportedly assisted by the student with whom he was having an affair.

A jogger found Khaw's wife and daughter Khaw Li-ling. Initially, the jogger thought the pair were taking a nap in their yellow Mini Cooper, which was parked on the side of the road near a bus stop. When she passed by again 45 minutes later and realized they hadn't moved, she called the police.

The mother and daughter were rushed to the nearby Prince of Wales Hospital, the same one where Khaw worked, and were declared dead.

The couple's domestic helper painted a picture of a strained marriage in her testimony on Thursday. She told the court that Khaw and his wife had been sleeping in separate rooms since she started working for them and their four children.

"Ma’am did the cooking for the children," Siti Maesaroh said. "Sir made [his own meals] for himself."

The couple drove their own cars, she said. Him, a Toyota. Her, the Mini Cooper.

"The last thing" Khaw wanted was for his daughter to die, prosecutors told the court. He may not have known that the teenager was not at school that afternoon.

When the pathologist testified on the postmortems conducted, Khaw burst into tears as the courtroom heard of the 16-year-old's death. Like her mother, she had lethal amounts of carbon monoxide in her blood.

While eyewitnesses at Hong Kong's Chinese University said Khaw claimed he was using the gas for an experiment, he later told police that he needed carbon monoxide to deal with a rat problem at home. His helper countered that there were no rats.

Then Khaw suggested his daughter may have used the inflatable balls to kill herself. Bruce, the prosecutor, called it "a lame lie."

The trial continues.

Write to Laignee Barron at [email protected].