WASHINGTON — At least two federal prosecutors involved in the botched ethics trial of the late Senator Ted Stevens “intentionally withheld and concealed” significant evidence from the defense team that could have resulted in his acquittal, a court-appointed investigator has concluded.

In a blistering 514-page report made public on Thursday, the special investigator said he had uncovered evidence that would “prove beyond a reasonable doubt” that two members of the prosecutorial team in the 2008 trial, Joseph W. Bottini and James A. Goeke, had deliberately kept exculpatory information from Mr. Stevens’s defense team.

But the report said that because the federal judge overseeing the trial, Emmet G. Sullivan, had not specifically ordered the government lawyers to turn over any such materials to the defense, as they are required to do by law, they could not be prosecuted for criminal contempt of court.

“Were there a clear, specific and unequivocal order of the court which commanded the disclosure of this information, we are satisfied that a criminal contempt prosecution” would be appropriate, the investigator, Henry F. Schuelke, and a colleague who assisted him, William Shields, concluded.