Former President Chen Shui-bian (R) is an ex-human rights lawyer
Taiwanese prosecutors have announced they are mounting a corruption inquiry against ex-President Chen Shui-bian.
The move came as he lost presidential immunity after being formally replaced by Ma Ying-jeou, two months after the latter's decisive election victory.
Prosecutors named Mr Chen as a suspect in a $450,000 embezzlement case. He any denies wrongdoing.
His wife, Wu Shu-chen, is already on trial in the same case, on charges of corruption and forgery.
Prosecutors said they had asked the presidential office for documents which had been kept confidential while Mr Chen, a former human rights lawyer, was in office.
"We have formally started the investigation of the special expenses case concerning former president Chen," said a spokesman for a special investigation unit of the Supreme Prosecutor's Office.
Mr Chen made no comment about the case during a visit on Tuesday to a recycling factory run by a Buddhist charity in the capital of Taipei.
Mr Chen and his family have been mired in corruption allegations since 2006, when his son-in-law was charged with insider trading on the stock market and then jailed for seven years.
An inquiry in 2006 sparked massive demonstrations calling for Mr Chen's resignation and moves in parliament to oust him from office.
The new Taiwanese president favours closer relations with the Chinese government.
In his inauguration speech, Mr Ma said he wanted a new dialogue with China, but denied he would enter reunification talks.
The softly-spoken politician has previously said he wants Taiwan to be regarded internationally as a responsible stakeholder and not a troublemaker.
The BBC's Caroline Gluck in Taipei says this is a dig at his predecessor, Mr Chen, whose strident pro-independence views not only angered China, but at times also strained relations with the island's most important ally, the US.