A former Credit Suisse broker charged with fraud in an auction rate securities scam may have fled to his native Bulgaria, the Wall Street Journal reported on Thursday, citing people familiar with the case.

The move comes as prosecutors prepare to bring criminal charges in a probe into activities of two former Credit Suisse brokers - Bulgarian-born Julian Tzolov and Eric Butler - claiming they lied to investors about how they placed money into short-term securities, the Journal said.

The two New York-based brokers resigned from Credit Suisse on September 7, 2007, the newspaper had said earlier this month. It had also said Credit Suisse is not a target of the investigation, according to people familiar with the matter.

The investigation involves the market for auction rate securities, which allow issuers such as municipalities and student loan companies, closed-end mutual funds or financial institutions to borrow money for the long term but at short-term, or lower, interest rates, according to the paper.

The probe is being conducted by the U.S. attorney's office for New York's Eastern District, the paper said. The Justice Department did not immediately return a call or an e-mail seeking comment.

Lawyers for Tzolov and Butler could not immediately be reached for comment.