Until about ten years ago, many states still had laws that required a police officer to witness an assault before making an arrest. Today, without having witnessed the event, officers in all states can arrest someone they suspect has committed a domestic assault. The majority of states have adopted preferred arrest policies which require police to either arrest one or both parties at the scene, or write a report justifying why an arrest is not made. Arrest policies do differ by jurisdiction, even in the same state. Some states -- such as New York, Wisconsin, and Minnesota -- have adopted mandatory arrest policies which dictate that an officer must make an arrest at a domestic situation. Such policies were adopted after it was realized how serious domestic situations could be for the victims and their children. An arrest is usually made after the following conditions have been satisfied:

• There is probable cause that a crime was committed;
• The suspect and the victim fit the definition of having a domestic relationship;
• The suspect's alleged act fits the definition of domestic assault;
• There is reason to believe that the domestic abuse will continue if the suspect is not arrested and/or there is evidence of injury;
• The incident was reported within 28 days of occurrence.

Usually, if none of these conditions are satisfied, the officer may use his or her discretion in deciding whether to make an arrest. Although different states have variations on definitions of domestic violence, most are similar to the following example.