Taiwan leader Chen Shui-bian's son-in-law was detained on Thursday after marathon questioning on suspicion of insider trading in a scandal that has sparked opposition calls for Chen's resignation.

Chao Chien-ming, a doctor married to Chen's daughter, was detained after prosecutors and the Bureau of Investigation questioned him for about 15 hours, Taipei prosecutor Lin Ban-liang said.

"A court approved Chao Chien-ming's incommunicado detention after prosecutors questioned him," Lin said by telephone.

Chen said in a statement late on Wednesday he would never cover up wrongdoing and that he "respected the judiciary's and the bureau's independence 100 percent".

Chao's parents, brother and sister-in-law were freed after questioning.

An opposition deputy has accused Chao of using dummy accounts to buy Taiwan Development Corp. shares from the partly state-owned Chang Hwa Bank at relatively low prices in a private placement last year.

Taiwan Development share prices have skyrocketed after a banking consortium bailed out the financially troubled real estate developer.

Su Teh-jien, chairman of Taiwan Development, and two other buyers have also been taken into court custody.

Some legislators from the main opposition Nationalist Party have called for Chen's ouster, but party chairman Ma Ying-jeou, who plans to run for president in 2008, said such a move was not feasible and would divert attention away from the scandal.