CNN

WASHINGTON (CNN) – The man who oversaw the flawed prosecution of corruption charges against former U.S. Sen. Ted Stevens of Alaska will leave his post at the Justice Department at the end of this week, a top official there announced Wednesday.

William Welch - who heads the Office of Public Integrity, which is responsible for investigating and prosecuting bribery and other public corruption cases - will leave Washington and become a federal prosecutor in Massachusetts, said Assistant Attorney General Lanny Breuer.

A federal judge harshly criticized the trial prosecutors for, among other things, failing to share certain evidence with the defense as required.

At the same time that U.S District Judge Emmet Sullivan set aside the conviction of Stevens in April, he initiated criminal contempt proceedings against Welch and the other government attorneys who prosecuted the 85-year-old Republican.

Sullivan appointed an independent, nongovernment attorney, Henry Schuelke III, to investigate. That investigation is still under way.

Despite the missteps, Breuer on Wednesday praised Welch and called his departure "a mutual decision."

"I think the world of him," Breuer said. "Bill and I have grown close, and we made a mutual decision. I think Bill believes it would be best for him on a personal level and best for the Criminal Division that, at this period of time, that he wants to go back to Boston where so much of his career was based."

The Office of Public Integrity, which Breuer described as "one of the great jewels of the Criminal Division," will be headed by an acting chief, Raymond Hulser, while the Justice Department conducts a nationwide search for a new chief to serve in the sensitive post.