In 1962 he was sworn in as an Assistant United States Attorney in the Southern District of New York, in the office led by Robert Morgenthau. He was a federal prosecutor for over three years and tried a number of major criminal cases. These included convicting, after a four-month trial, five officials of a federal savings and loan association of perjury. The perjury was committed by the bank officers to cover up the diversion of over $250,000 from the savings and loan association to finance a political campaign for Congress being conducted by the president of the association. He also won a jury verdict convicting a prominent accountant and investor of bribing and conspiring (with other major investors) to bribe an internal revenue agent.