171.137. Arrest required for suspected battery constituting domestic violence; exceptions.
1. Except as otherwise provided in subsection 2, whether or not a warrant has been issued, a peace officer shall, unless mitigating circumstances exist, arrest a person when he has probable cause to believe that the person to be arrested has, within the preceding 24 hours, committed a battery upon his spouse, former spouse, any other person to whom he is related by blood or marriage, a person with whom he is or was actually residing, a person with whom he has had or is having a dating relationship, a person with whom he has a child in common, the minor child of any of those persons or his minor child.
2. If the peace officer has probable cause to believe that a battery described in subsection 1 was a mutual battery, he shall attempt to determine which person was the primary physical aggressor. If the peace officer determines that one of the persons who allegedly committed a battery was the primary physical aggressor involved in the incident, the peace officer is not required to arrest any other person believed to have committed a battery during the incident. In determining whether a person is a primary physical aggressor for the purposes of this subsection, the peace officer shall consider:
(a) Prior domestic violence involving either person;
(b) The relative severity of the injuries inflicted upon the persons involved;
(c) The potential for future injury;
(d) Whether one of the alleged batteries was committed in self-defense; and
(e) Any other factor that may help the peace officer decide which person was the primary physical aggressor.
3. A peace officer shall not base his decision regarding whether to arrest a person pursuant to this section on his perception of the willingness of a victim or a witness to the incident to testify or otherwise participate in related judicial proceedings.
4. As used in this section, “dating relationship” means frequent, intimate associations primarily characterized by the expectation of affectional or sexual involvement. The term does not include a casual relationship or an ordinary association between persons in a business or social context.