WASHINGTON -- As the Watergate break-in nears its 40th anniversary, the Justice Department has filed a brief in federal district court opposing a historian's bid to unseal records that would shed light on one of the scandal's last remaining mysteries: what was overheard on the illegal wiretap that led to the resignation of President Richard Nixon....

Secret tape recordings made in the Oval Office and other evidence uncovered by investigating committees and special prosecutors helped unravel the cover-up and triggered Nixon's August 1974 resignation....

In May 2009, history professor Luke A. Nichter, of Texas A&M University, wrote to the US District Court in the District of Columbia, seeking to persuade Chief Judge Royce C. Lamberth to release long-sealed records from the original trial of the five burglars and their two superiors, G. Gordon Liddy and the late E. Howard Hunt. ...