If, on investigation before such mayor or justice of the peace, it shall appear that any person has violated the law against unlawful retailing or giving away of intoxicating liquors, or that any person is unlawfully keeping intoxicating liquors, it shall be the duty of such mayor or justice of the peace, upon affidavit being made, to issue his warrant for the person or persons supposed to be guilty and dispose of the same as other criminal prosecutions before a mayor or justice of the peace under the laws of the state.