When police respond to a partner or family member assault complaint and it appears that both people used force, Montana law directs the officer to determine who was the predominant aggressor. If the officer determines that one person is, the officer may arrest only that person (MCA § 46-6-311(2)(b)). The rule does not guarantee that only one person is arrested. This page is part of our Montana Domestic Violence Guide.
What the Statute Says
The rule is two sentences long. First: "When a peace officer responds to a partner or family member assault complaint and if it appears that the parties were involved in mutual aggression, the officer shall evaluate the situation to determine who is the predominant aggressor." Second: "If, based on the officer's evaluation, the officer determines that one person is the predominant aggressor, the officer may arrest only the predominant aggressor."
The same statute says that arrest is "the preferred response" in partner or family member assault cases involving injury, use or threatened use of a weapon, violation of a restraining order, or other imminent danger (§ 46-6-311(2)(a)). That is a stated preference. It is not written as a requirement that someone be arrested on every call. See does someone have to go to jail.
The Six Listed Considerations
The determination "must be based on but is not limited to" these, "regardless of who was the first aggressor":
| § 46-6-311(2)(b) | Consideration |
|---|---|
| (i) | The prior history of violence between the partners or family members, if information about it is available to the officer |
| (ii) | The relative severity of injuries received by each person |
| (iii) | Whether an act of or threat of violence was taken in self-defense |
| (iv) | The relative sizes and apparent strength of each person |
| (v) | The apparent fear or lack of fear between the partners or family members |
| (vi) | Statements made by witnesses |
Because the list is "not limited to" these items, an officer can take other things into account. Our page on predominant aggressor factors looks at each one and at how it tends to be documented.
Can Both People Still Be Arrested?
The statute speaks to one situation: the officer determines that one person is the predominant aggressor. Then only that person may be arrested. It is silent about the case where the officer evaluates the scene and cannot say that either person was predominant. Nothing in the text expressly bars arresting both in that situation, and the general rule that an officer may arrest on probable cause when circumstances require immediate arrest still applies (§ 46-6-311(1)).
So dual arrests can happen. How often they do, and how a particular agency trains its officers, is not something the statute answers.
An Arrest Decision Is Not a Finding of Guilt
The officer's choice is made quickly, often at night, with two upset people giving different accounts. It decides who goes to jail that evening. It does not decide the case. The prosecutor reviews the reports and decides what to charge, and at trial the State must prove each element beyond a reasonable doubt.
If you were the one arrested, that means the predominant aggressor call can be tested. The same considerations the officer weighed, such as injuries, size, fear, and witness statements, are things the evidence can be checked against. And if you acted to protect yourself, self-defense is a legal justification, not only an arrest factor. A person is justified in using force when and to the extent the person reasonably believes it is necessary for self-defense against another's imminent use of unlawful force (MCA § 45-3-102). See self-defense in a PFMA case.
If Both of You Are Charged
Two cases from one incident create problems that a single case does not:
- You are each a defendant and a witness. What you say about the other person's conduct may also describe your own. Each of you has the right not to incriminate yourself, and each of you needs advice from your own lawyer before making statements.
- Each of you may be a protected person. A no contact order can run in both directions. Follow yours exactly, even if the other person reaches out. See if the protected person contacts you.
- Housing and children need a plan. If you share a home or children, the orders control who can be where.
Do not try to agree with the other person on what to tell the court or the prosecutor. That can lead to new allegations, and it can violate a no contact order.
Why the Label Follows the Case
The predominant aggressor determination shows up again in one other place. A person who commits PFMA in the presence of a child can be charged with endangering the welfare of children, but "only the predominant aggressor, as determined by 46-6-311, may be charged" under that provision (MCA § 45-5-622(4)(c)). See PFMA in front of children.
If you called for help and were arrested anyway, read if you called the police and got arrested. If you are in danger, call 911. The National Domestic Violence Hotline is 1-800-799-7233. A&M Law defends PFMA charges in Western Montana: see our PFMA defense page.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal advice about your specific case.