delivered the opinion of the Court:
Plaintiff in error was convicted of an assault with intent to commit murder, and sentenced to the penitentiary for the term of five years. The fact that he committed an assault with a deadly weapon, and without any legal excuse, is proved beyond doubt, and is not controverted. The sole defence interposed upon the trial was, that plaintiff in error was insane at the time of the committing of the assault. Evidence was introduced on behalf of plaintiff in error, and of the People, upon this issue, so that the question was fairly before the jury.' Of the weight of that evidence we do not deem it our province; in the present state of the case, to speak. Plaintiff in error was entitled to have the issue passed upon by the jury, and that they might do so intelli*20gently and dispassionately, it was indispensable that,irrelevant evidence tending to complicate the issue or improperly arouse their prejudices should be excluded.
Before the trial, plaintiff in error moved to continue the cause on account of the absence of a material witness, and in his affidavit in support of that motion he deposed that he could prove by the absent witness that he did not fire the shot which constituted the alleged murderous assault, and that what he could so prove was true, and that he was not guilty, etc. The court overruled the motion, and refused to continue the cause. On the trial, and after the People had given to the jury all their evidence in rebuttal of the evidence of the plaintiff in error on the question of insanity, the State’s attorney was permitted by the court, over the objection of the plaintiff in error, to read this affidavit in evidence to the jury. It is patent that it was utterly irrelevant to the issue being tried. It did not tend to prove a single fact which it was incumbent on the People to prove, or to disprove anything which the plaintiff in error had attempted to prove. Of course, the affidavit of the party is competent evidence against himself, when it is relevant to the issue. It stands on the same footing as any other declaration made by him under oath. But who would pretend that it would be relevant on the question of insanity to prove that a party had, before that time, declared his innocence of any particij)ation in the act alleged to be criminal, and had sworn to this declaration ? The affidavit may be true, and the plaintiff in error may have also been' insane. If" he was in fact insane, he may have had no recollection of the transaction, or no capacity to reason in regard to it. In any view, what he swore to in this affidavit can not have a tendency to enlighten the question whether he was affected with insanity at the time he committed the assault. The improper effect of the affidavit upon the minds of the jury may have been either in producing the belief that the defence of insanity was an *21afterthought, and so not urged in good faith, or that plaintiff in error had committed perjury in making the affidavit, for which he deserved punishment. If he was really insane when he committed the assault, it could legally make no difference when the defence was first interposed. He would not, himself, be a competent judge of his mental status, and the more certain his insanity, the more certain it would be that his affidavit ought not to be regarded, for any purpose. But the proof that he committéd the assault being conclusive, the jury, without reflecting whether sane or insane, might conclude he is clearly guilty of perjury, and use the fact of that guilt not only as a make-weight in determining his guilt of the specific offence charged, but also in fixing the amount of his punishment for that offence. If it be true that he committed perjury in the affidavit, he can not be punished for that offence on this trial. These principles are obvious, and can require no elaboration.
For the error in admitting the affidavit in evidence, the judgment below is reversed, and the cause remanded. The other errors assigned are not deemed tenable.
Judgment reversed.