It is a different thing to engage as private counsel in a prosecution against a man whom he knows or believes to be innocent. Public prosecutions are carried on by a public officer, the Attorney-General, or those who act in his place; and it ought to be a clear case to induce gentlemen to engage on behalf of private interests or feelings, in such a prosecution. It ought never to be done against the counsel's own opinion of its merits. There is no call of professional duty to balance the scale, as there is in the case of a defendant. It is in every case but an act of courtesy in the Attorney-General to allow private counsel to take part for the Commonwealth; such a favor ought not to be asked, unless in a cause believed to be manifestly just. The same remarks apply to mere assistance in preparing such a cause for trial out of court, by getting ready and arranging the evidence and other matters connected with it: as the Commonwealth has its own officers, it may well, in general, be left to them. There is no obligation on an attorney to minister to the bad passions of his client; it is but rarely that a criminal prosecution is pursued for a valuable private end, the restoration of goods, the maintenance of the good name of the prosecutor, or closing the mouth of a man who has perjured himself in a court of justice. The office of Attorney-General is a public trust, which involves in the discharge of it, the exertion of an almost boundless discretion, by an officer who stands as impartial as a judge. "The professional assistant, with the regular deputy, exercises not his own discretion, but that of the Attorney-General, whose _locum tenens_ at sufferance, he is; and he consequently does so under the obligation of the official oath."[16] On the other hand, if it were considered that a lawyer was bound or even had a right to refuse to undertake the defence of a man because he thought him guilty, if the rule were universally adopted, the effect would be to deprive a defendant, in such cases, of the benefit of counsel altogether.