By Luisa Beltran, CBS.MarketWatch.com Last Update: 2:12 PM ET May 3, 2004 NEW YORK (CBS.MW) - Frank Quattrone, the once powerful Credit Suisse First Boston investment banker, was convicted Monday of obstructing a federal probe into the allocation of IPO shares at his former employer CS First Boston. Quattrone was convicted of two counts of obstructing justice and one count of witness tampering for sending a Dec. 5, 2000 email encouraging employees of CSFB to "clean up" their files. He faces a maximum of 25 years in prison. Sentencing was set for September 8. Quattrone will remain free on bail in the interim. The trial was the second for Quattrone. Late last year, a jury failed to reach a verdict and U.S. District Judge Richard Owen granted a mistrial. The second trial began April 13 with jury selection. The proceedings we're notable for some significant changes from the first. During the second trial , the defendant said he did take part in the allocation of IPOs but did not have overall decision making power. During the first, he claimed to have nothing to do with IPO allocation. Also, Quattrone now claims to have some idea of what a grand jury is. In the first, he said he did not know what a grand jury did. Quattrone, 48, also surprised many when he took the stand during the second trial. During the first, he came off as argumentative and hedged on his responses in cross examination. But in the second, Quattrone appeared poised and calm. Luisa Beltran is a reporter for CBS.MarketWatch.com in New York.