The two prosecutions under investigation are those of Dr. Cyril Wecht, a well-known forensic pathologist who served for many years as coroner in Allegheny County, the Pittsburgh area, and former Alabama Gov. Don Siegelman.

Wecht's trial ended in a hung jury, and an appeals court has delayed a retrial. Siegelman is fighting to overturn his conviction, and an appellate court ordered his release on bail.

The committee sent a nine-page subpoena seeking documents on both cases and communications between the White House, prosecutors, members of Congress and others.

Wecht's lawyer, Dick Thornburgh, who served as U.S. attorney general under President George H.W. Bush, testified before the committee that he believes the prosecution was politically motivated.

The committee chairman, Rep. John Conyers, D-Mich., said that a subpoena was necessary because the Justice Department has been "unresponsive" to requests for information.