Washington ? A seething federal judge dismissed the corruption conviction of former Alaska Sen. Ted Stevens on Tuesday and took the rare and serious step of ordering a criminal investigation into prosecutors who poisoned 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 withheld evidence from defense attorneys and the judge 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, 85, a Senate seat he had held for 40 years. Once the Senate’s longest-serving Republican, he narrowly lost to Democrat Mark Begich soon after the verdict.

Now, the case could prove career-ending for prosecutors in the Justice Department’s public corruption unit.

After Sullivan dismissed the case, Stevens turned to his friends and held up a fist in victory as his wife and daughters broke into loud sobs.

“Until recently, my faith in the criminal system, particularly the judicial system, was unwavering,” Stevens told the court Tuesday, his first public comments since Attorney General Eric Holder announced he would drop the case. “But what some members of the prosecution team did nearly destroyed my faith. Their conduct had consequences for me that they will never realize and can never be reversed.”

The unraveling of the case overshadowed the facts of a trial in which Stevens was shown to have accepted thousands of dollars in undisclosed gifts.

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

Sullivan said the misconduct was too serious to be left to an internal investigation by the Justice Department, which he said dragged its feet before investigating. He criticized former Attorney General Michael Mukasey for not responding to complaints: “Shocking, but not surprising,” Sullivan said.

He worried aloud about how often prosecutors withhold evidence.