If, in the effort to suppress or disperse any unlawful or riotous assembly, or to arrest or detain any of the persons engaged in the assembly, any of the rioters or other persons then present as spectators or otherwise are killed or wounded, the district judge, magistrate, and officers and persons acting in their aid are guiltless of the killing or wounding. However, if a district judge, magistrate, or officer or person acting in their aid is killed or wounded, all the persons unlawfully engaged in the assembly are guilty of the killing or wounding.