Results of the investigation were made public Monday. The report singled out the removal of U.S. Attorney David Iglesias of New Mexico - among 9 prosecutors who were fired - as the most troubling.
Republican political figures in New Mexico, including Sen. Pete Domenici and Rep. Heather Wilson, had complained about Iglesias' handling of voter fraud and public corruption cases, and that led to his firing, the report said.
Justice Department Inspector General Glenn Fine and Office of Professional Responsibility director Marshall Jarrett said that a prosecutor was needed because "serious allegations involving potential criminal conduct have not been fully investigated or resolved."
Potential crimes described in their report include lying to investigators, obstruction of justice and wire fraud.
Domenici's spokesman did not immediately return a call Monday from The Associated Press and a Wilson spokesman reached Monday morning declined to comment immediately. Both lawmakers are leaving Congress at the end of the year.
Mukasey named Nora Dannehy, a career prosecutor, to direct the probe.
Investigators said they do not have the complete story of the firing of Iglesias, blaming it on the refusal of Domenici, former White House adviser Karl Rove, former White House counsel Harriet Miers, former Justice Department official Monica Goodling and other key witnesses still to be interviewed.
The report describes an almost total lack of involvement by former Attorney General Alberto Gonzales and his deputy, Paul McNulty, in decisions to force out nine U.S. prosecutors, who are political appointees but who may not be dismissed for improper reasons.
The report described as "remarkable" Gonzales' and McNulty's apparent ignorance of the reasons for the firing of U.S. Attorney Daniel Bogden of Nevada.
Gonzales "bears primary responsibility" for the process of firing of the prosecutors and the turmoil that followed, the report said. He "abdicated" his leadership role and was "remarkably unengaged," it said.
But the report concluded that Gonzales' chief of staff, Kyle Sampson, was the person most responsible for coming up with the plan to fire the prosecutors and said that Sampson's comments to Congress, the White House and others were misleading.
Despite claims by Sampson and others that the firings were for poor performance, the 358-page report found that Bud Cummins, the U.S. Attorney in Arkansas, was forced out to make way for Timothy Griffin, who had served as Rove's deputy in the White House political office.
It also said that the dismissal of Todd Graves, the U.S. Attorney for the Western District of Missouri, probably resulted from pressure from the office of Republican Sen. Christopher "Kit" Bond. Bond was upset that Graves did not intervene in a dispute between the staffs of Bond and Republican Rep. Sam Graves, the prosecutor's brother, the report said.
Investigators found no evidence that Arizona U.S. Attorney Paul Charlton and U.S. Attorney Carol Lam of San Diego were fired for prosecuting Republican members of Congress.
Similarly, Justice Department officials had legitimate concerns about the work of two other prosecutors who were fired, Margaret Chiara of Grand Rapids, Mich., and Kevin Ryan of San Francisco, the report said.
