The head of the Justice Department's anti-corruption unit is stepping down after the office's botched trial of former Alaska Sen. Ted Stevens.

The public integrity unit has been under intense scrutiny since the conviction of Stevens, an Alaska Republican, was thrown out due to key evidence being withheld from his defense.

William Welch's departure is "a mutual decision," said Welch's boss, Lanny Breuer. Welch plans to remain a federal prosecutor, but will relocate to Massachusetts. Breuer also praised Welch as "an extraordinary person."

A few of the prosecutors who worked on the Stevens case have already taken other positions, and there are two separate investigations into how the case was handled.