Taiwanese authorities Thursday charged a former top security chief with concealing documents that hampered investigations into alleged money laundering implicating former president Chen Shui-bian.

"We have sought a jail sentence of two and a half years against Yeh Sheng-mao for hiding important documents that resulted in prosecutors losing their optimal time in their probes into the alleged money laundering case," said chief prosecutor Lin Chin-chun in a news conference.

Lin said the documents concerning alleged money laundering by Chen's wife, Wu Shu-chen, were submitted by the head of the anti-money laundering centre to Yeh, who was then director of the Investigation Bureau, in February this year.

Yeh later told the centre head he already personally handed the documents to prosecutor-general Chen Tsung-ming for further investigation and necessary legal action.

Yeh never passed on the documents, claiming later he forgot as he was busy during the transition between governments. He said he had verbally told the prosecutor-general about the issue, but Chen Tsung-ming denied the claim.

Lin said on August 21 prosecutors searched the home of Yeh and found copies of the documents, indicating that it is unlikely Yeh forgot about them

Yeh is the first person to have been indicted in the snowballing money laundering scandal involving the former persident.

The allegations surfaced in June when Swiss judicial authorities alerted Taiwan of suspected money laundering after detecting unusual fund transfers in the bank accounts set up by Swiss banks in the Cayman Islands for former president Chen's son, Chen Chih-chung, and daughter-in-law, Huang Jui-ching.

However, it took almost a month before Taiwan's envoy to Switzerland, who was appointed by Chen, to send the alert to Taiwan's Foreign Ministry, which transferred the case to the Justice Ministry on July 30 for investigation.

The scandal was first revealed by a Taiwan magazine on August 10. On August 14, Chen admitted that his wife Wu Shu-chen had remitted 21 million US dollars - campaign funds from the 2000 and 2004 presidential election that Chen had not declared - into several foreign bank accounts.

But he insisted that the funds were not laundered money, and prosecutors later discovered that Wu had asked her brother, Wu Ching-mao, son and daughter-in-law to set up overseas bank accounts for her to wire the money to.

Prosecutors have questioned Chen, his wife, brother-in-law, son and daughter-in-law over their alleged roles in the scandal and barred them from leaving Taiwan, pending further questioning.

Taiwan has also acquired legal assistance from Switzerland and Singapore - destinations where Wu allegedly wired the money.

Chen stepped down as president in May after serving two four-year terms from 2008. He was succeeded by Ma Ying-jeou of the Nationalist Party or Kuomintang.