At common law, persons convicted of infamous crimes were incompetent as witnesses. Infamous crimes are generally denned to be those punishable by death or imprisonment in the penitentiary. The reason was, that men who have been guilty of such heinous crimes had become so depraved as to be unworthy of belief; that the individual has sunken so low in the moral realm as to be insensible to the sanctity of an oath, and to be reckless in the handling of truth; that the credit of his oath is overcome by the stain of his iniquity. To disqualify him, even at common law, however, he must have been adjudged guilty of such crime. It is the record of the judgment of a court of competent jurisdiction, passing sentence upon him, that disqualifies him as a witness. Such witness could testify, however, in his own behalf.

This disqualification has generally been removed by statute, but it may be shown as strongly affecting the credibility of the witness.8