WASHINGTON A federal judge dismissed the corruption conviction of former Alaska Sen. Ted Stevens today and took the rare and serious step of opening a criminal investigation into prosecutors who mishandled the case.

"In nearly 25 years on the bench, I've never seen anything approaching the mishandling and misconduct that I've seen in this case," U.S. District Judge Emmet Sullivan said.

Sullivan appointed a special prosecutor to investigate Justice Department lawyers who repeatedly mishandled witnesses and withheld evidence from defense attorneys during the monthlong trial. Stevens was convicted in October of lying on Senate forms about home renovations and gifts he received from wealthy friends.

The case cost Stevens a Senate seat he had held for 40 years.

Sullivan appointed Washington attorney Henry Schuelke as a special prosecutor to investigate contempt and obstruction by the Justice Department team. Schuelke is a former prosecutor and veteran defense attorney who was tapped to oversee a Senate Ethics Committee investigation into influence-peddling allegations against former New York Sen. Alfonse D'Amato in 1989.

Sullivan said the matter was too serious to be left to an internal investigation by the department, which he said has dragged its feet looking into the misconduct.

He criticized former Attorney General Michael Mukasey for not responding to complaints of misconduct in the case.

By The Associated Press