I recently visited the United States Attorney (EDNC) website, and came upon this quotation:
The United States Attorney is the representative not of an ordinary party to a controversy, but of a sovereignty whose obligation to govern impartially is as compelling as its obligation to govern at all; and whose interest, therefore, in a criminal prosecution is not that it shall win a case, but that justice shall be done. As such, he is in a peculiar and very definite sense the servant of the law, the twofold aim of which is that guilt shall not escape or innocence suffer. He may prosecute with earnestness and vigor — indeed, he should do so. But, while he may strike hard blows, he is not at liberty to strike foul ones. It is as much his duty to refrain from improper methods calculated to produce a wrongful conviction as it is to use every legitimate means to bring about a just one.
It’s important to remember that what occasioned those lofty sentiments was the case of Berger v. United States, 295 US 78 (1935) in which Berger was illegally convicted because, as the Supreme Court said:
That the United States prosecuting attorney overstepped the bounds of that propriety and fairness which should characterize the conduct of such an officer in the prosecution of a criminal offense is clearly shown by the record. He was guilty of misstating the facts in his cross-examination of witnesses; of putting into the mouths of such witnesses things which they had not said; of suggesting by his questions that statements had been made to him personally out of court, in respect of which no proof was offered; of pretending to understand that a witness had said something which he had not said and persistently cross-examining the witness upon that basis; of assuming prejudicial facts not in evidence; of bullying and arguing with witnesses; and in general, of conducting himself in a thoroughly indecorous and improper manner. We reproduce in the margin a few excerpts from the record illustrating some of the various points of the foregoing summary. It is impossible, however, without reading the testimony at some length, and thereby obtaining a knowledge of the setting in which the objectionable matter occurred, to appreciate fully the extent of the misconduct. The trial judge, it is true, sustained objections to some of the questions, insinuations and misstatements, and instructed the jury to disregard them. But the situation was one which called for stern rebuke and repressive measures and, perhaps, if these were not successful, for the granting of a mistrial. It is impossible to say that the evil influence upon the jury of these acts of misconduct was removed by such mild judicial action as was taken.