Earl J. Silbert was in bed when the telephone rang early in the morning of June 17, 1972, rousing him from his sleep.

A colleague was on the other end of the line, calling to inform Mr. Silbert, then the principal assistant U.S. attorney for the District of Columbia, of the strange events that had transpired hours earlier at the Watergate complex on the banks of the Potomac River. Five men wearing business suits had been arrested in an attempt to bug the headquarters of the Democratic National Committee. One of them was James W. McCord Jr., the security chief for President Richard M. Nixon’s reelection campaign and a former CIA employee.