TAIPEI, TAIWAN - The son and daughter-in-law of former Taiwan president Chen Shui-bian protested their innocence on Monday, as they returned home as part of a probe into alleged money-laundering by Chen and his family.

Chen Chih-chung and his wife Huang Jui-ching are suspected of laundering millions of dollars for the ex-president through overseas bank accounts, but Chen said he had only done what his mother had asked them to do.

"My mother manages the family's money," he told reporters at the airport after returning from New York. "We do what my mother wants us to do."

Copies of Swiss documents obtained by a Taiwanese lawmaker showed Chen Chih-chung and his wife had transferred 31 million US dollars to Swiss bank accounts in 2007. They are expected to be questioned this week.

The couple flew to the United States this month just days before Taiwan authorities launched a probe into money laundering claims implicating the former first family, following similar moves by Swiss authorities.

Chen Shui-bian, his wife, son, daughter-in-law and brother-in-law have all been named defendants in the money laundering case.

The ex-president has admitted that his wife had wired 20 million US dollars abroad from his past campaign funds, but said she had done so without his knowledge. He has denied any illegal activity.

Chen is already being investigated for allegedly embezzling 14.8 million Taiwan dollars (480,500 US) in special expenses while president, and his wife is on trial for corruption and document forgery in the same case.