A radio station chief and his wife from Yunnan Province killed their 25-year-old son because a secret they had kept hidden was about to be revealed, it was reported Sunday.

Early on the morning of January 5, Zhang Xiaoyu and his wife Wen Xiuping turned on a gas container in Zhang Li's room when their son was asleep and locked all the windows and doors.

Zhang Li was woken by the pungent smell and tried to escape. He managed to call the police but his parents then beat him repeatedly on the head. The parents had been detained on a charge of murder, the Yunnan-based Life News reported yesterday.

The couple's friends expressed shock at the news as Zhang, founder and chief of the Lincang People's Broadcasting Station, was said to be "always kind to everyone around and never gets angry with anyone while Wen is a typical devoted wife and loving mother," according to the news report.

The secret that the parents had been keeping to themselves for more than 10 years was that their son suffered from intermittent mental illness. Zhang Li had to take pills every day but this failed to control his condition.

"At first, our son only liked to talk nonsense. Then he began to curse people frequently," the newspaper quoted his father as saying.

At the cremation of their son, Zhang cried out: "You have once threatened to kill people. We would rather kill you first before you kill others."

Zhang was also concerned the secret he and his wife had endeavored to keep would be revealed when the son married his girlfriend, who had not been aware of the disease.