A Swiss lawyer conspired to stash a Virginia doctor's cash in Swiss bank accounts to avoid paying taxes in the United States, prosecutors allege.

Felix Mathis, a Zurich-based lawyer at Froriep Renggli LLP, helped Dr. Andrew Silva, of Sterling, conceal from U.S. authorities foreign bank accounts and funds sent here, according to an indictment filed last week at federal court in Alexandria.

A warrant has been issued for Mathis' arrest, but he is not yet in U.S. custody.

The pair used a sham Liechtenstein trust to hide the existence of the Swiss accounts, according to the indictment.

Mathis instructed Silva to keep the account "hush-hush" and to not maintain any records of its existence, the indictment said. If Silva wanted to talk to Mathis about the Swiss accounts, he should send a coded letter requesting to "meet for coffee," prosecutors say.

In September 2009, according to court documents, Silva was told that the bank was closing the account.

Mathis allegedly told Silva he should not wire transfer the funds back to the United States because it would leave a paper trail for U.S. authorities.

Instead, Mathis and an unidentified Swiss banker instructed Silva to mail the money to the United States in amounts of less than $10,000 in order to avoid declaring the money to U.S. officials, the indictment said.

With Mathis' help, prosecutors say, Silva sent about $235,000 to the U.S. in a manner that purposefully evaded monetary reporting requirements.

If Mathis is convicted, he will face up to 25 years in prison and a $1.25 million fine. His attorney, Patrick O'Donnell, did not return a call for comment.

Silva pleaded guilty in February to conspiring to defraud the United States. He is cooperating with prosecutors and was sentenced in June to two years of probation.

The bank is only identified in court documents as "one of the largest international banks," with headquarters in England and offices in Switzerland and Virginia. That bank was reported to be HSBC during the proceedings against Silva, but a spokesman for the U.S. Attorney's Office in Alexandria said he couldn't comment on the bank's identity.