Taiwan's Justice Ministry said its Swiss counterpart has requested assistance in an investigation into possible money laundering involving accounts held by the son and daughter-in-law of former president Chen Shui-bian.
The ministry said it received the request involving Chen's son, Chen Chih-chung, and daughter-in-law, Huang Jui-ching, via Taiwan's Foreign Ministry on July 31, according to a statement released late on Thursday.
It said local investigators were assisting in the case.
The ministry released its statement the same day Chen held a news conference to say his wife, Wu Shu-chen, had transferred some of his leftover funds from past presidential and mayoral campaigns to offshore accounts.
"Wu Shu-chen at the beginning of this year admitted that she had sent a portion of leftover campaign funds abroad and didn't let me know," he said. "It was meant to be for my use after leaving office."
On Friday, Chen resigned from his Democratic Progressive Party (DPP).
"Today it is with great sadness that I apologize to all party members and supporters," Chen said in a statement. "I have disappointed and shamed everyone, and failed to meet everyone's expectations, doing irreparable harm to the party."
It was not immediately clear if the investigation into possible money laundering is linked to money transfers by Chen's wife.
Chen, who left office in May due to term limits, and his wife are also part of an unrelated case in which they are being investigated over allegations of improper use of government funds.
Chen's popularity plunged in his final year in office, amid several scandals involving himself and various staff and family members, resulting in resounding defeats for the DPP in legislative and presidential polls earlier this year.
Chen resigned his post as DPP chairman in January after the party suffered its defeat in the legislative election, in which the opposition won 72% of seats in parliament while the DPP won just 24%.