Taiwan leader Chen Shui-bian's son-in-law was detained Thursday on suspicion of insider trading, prosecutors said.

Chao Chien-ming, a doctor married to Taiwan leader Chen Shui-bian's daughter, is escorted by Bureau of Investigation agents in Taipei May 24, 2006. Chao and four members of Chen's family were questioned on Wednesday by Bureau of Investigation agents probing a snowballing insider trading scandal. [Reuters]

Investigators questioned Chao Chien-min, his parents, brother and sister-in-law on Wednesday about the purchase of shares in ailing Taiwan Development Corp. The stock's value skyrocketed shortly after the purchase was made.

Early yesterday, a court released Chao's relatives but approved prosecutors' request to keep Chao under detention.

"There is a strong suspicion of his involvement in insider trading," said Lin Pang-liang, a spokesman for the Taipei Prosecutors' Office. Chao has denied the allegation.

Chen is already on the defensive over scandals that have rocked both his family and his Democratic Progressive Party administration.

Opposition politicians have accused Chen's wife, Wu Shu-chen, of receiving free vouchers from the new management of Taipei's Sogo Department Store and questioned her role in its takeover by a businessman whose bid was not the highest.

Taiwanese television stations have repeatedly shown footage of Wu using Sogo vouchers to pay for designer clothes and other expensive items shortly after the 2002 takeover. Chen's office has denied Wu received gifts in connection with the Sogo deal, saying she paid for the vouchers herself.

Another scandal involves Hsieh Ching-chih, vice chairman of the Science Council, whom police detained on Wednesday on suspicion that he illegally profited from an engineering contract in a high-speed rail project.

But Chao's case may prove the most disruptive of all. Two businessmen allegedly involved in the affair were detained last week. A court also approved detention of Taiwan Development Chairman Su Teh-chien yesterday.