Taiwan's judicial authority confirmed on Thursday that the Swiss judicial authorities had sought Taiwan's assistance in probing the source of money belonging to Chen's son and daughter-in-law, as they suspected it could be a money-laundering case. Inspectors left Taiwan for Switzerland on Tuesday to further investigate the case.
On Tuesday, Taiwan prosecutors questioned Chen for a second time over his alleged role in a special government fund embezzlement case.
The Taiwan authorities on August 6 declassified documents relating to Chen's use of special expenses, saying they contained no secrets.
Chen ended his tenure as Taiwan's leader in May.
Chen's admission concerning the funds transfer became headline news and a prominent item in TV broadcasts. Some media commentators urged that Chen be detained, since he and his family had repeatedly told the public that they had no overseas bank accounts and all their assets had been declared.
It also emerged that Chen's son and daughter-in-law had left Taiwan for the United States last Saturday.
The timing of their departure was "very unusual," said an inspector.