Relatives beat a Malaysian couple to death in a ritual apparently meant to help the man to stop smoking, police said Friday.

The couple died of head injuries after being beaten with broomsticks and motorbike helmets during a family gathering at a Kuala Lumpur home Wednesday, said Ku Chin Wah, head of the city’s crime investigations department.

One of the couple’s sons and three other relatives remain in custody. Four other detained family members have been released, Ku said.

According to those detained, a nephew suggested the beating ritual after the man said he could not stop smoking and the woman complained of a liver ailment, Ku said.

It is not clear who was responsible for the deaths, but local media reported that the nephew convinced all the members of the Muslim family to beat each other.

The couple’s 15-year-old niece, also injured in the beating ritual, has been hospitalized, Ku said. Several others, including the couple’s children, who are 14, 19 and 21 years old, also suffered injuries.

Police are still investigating the case. Local media reported the families are believed to have joined a cult recently, but that could not be immediately confirmed.