Stevens said on Tuesday that before his trial his faith in the US criminal justice system was "unwavering" but the actions of the prosecution team did "nearly destroyed my faith".

"Their conduct had consequences for me that they will never realise and can never be reversed," he said outside the court in Washington DC following the judge's decision to overturn his conviction, adding that Tuesday's move had "restored" his faith. 

Stevens, the Republican party's longest serving senator, lost his senate seat in last year's November elections.

'Tainted verdict'

Stevens' trial was beset by government errors, with the judge at one point holding three justice department lawyers in contempt for failing to turn documents over to Stevens' legal team.

In court documents, the department admitted it had not turned over notes from an interview with the oil executive, who estimated the value of the renovation performed on Stevens' home as far less than he testified at trial.

Eric Holder, the US attorney general, said last week the justice department's office of professional responsibility, a unit that investigates allegations of prosecutorial misconduct, would also review the case.

But Sullivan said on Tuesday he appointed Schuelke because the matter was too serious to be left to an internal investigation by the Justice Department, which he said had delayed looking into the misconduct.

Stevens was a ranking member of the senate appropriations committee and known for his ability to bring federal funding to Alaska, a sparsely populated state.