Josef Dorig admitted he engaged in a "wideranging" conspiracy between 1997 and 2011 to help US citizens evade income taxes by concealing assets in Credit Suisse accounts held in the names of sham entities, the Justice Department said.

The 72-year-old Swiss and Italian citizen pleaded guilty to one criminal count in a Virginia court and, if convicted, faces up to five years in prison.

"This plea sends a strong message to those who use or help others use offshore bank accounts to evade US taxes," Assistant Attorney General Kathryn Keneally said.

"We are receiving information from a variety of sources and are committed to investigating and prosecuting this wrongdoing."

Dorig also agreed to cooperate with investigators in the ongoing probe.

From 1972 through 1996, Dorig worked for a subsidiary of Credit Suisse that formed and maintained sham tax-haven entities. In 1997, the Credit Suisse subsidiary spun off these sham entities into a trust company, Dorig Partner AG, owned and operated by Dorig, the Justice Department said.

Credit Suisse promoted Dorig Partner, which sublet space from the bank in an office tower where one of its units was the major tenant.

Dorig was listed in a July 2011 Justice Department indictment that charged him and seven former Credit Suisse employees. In March, former Credit Suisse banker Andreas Bachmann, who was also listed in the 2011 indictment, pleaded guilty.

Credit Suisse has been in talks with the Justice Department to settle a probe over its role in enabling US customers to evade taxes. US prosecutors have reportedly pressed for a guilty plea from a Credit Suisse subsidiary.

The Justice Department has described a decades-long conspiracy that resulted in secret accounts for US customers with as much as $3 billion in total assets.

"The conspiracy dates back to 1953 and involved two generations of US tax evaders including US customers who inherited secret accounts" at Credit Suisse, it said in a July 2011 news release.