Justification: Law Enforcement

A law enforcement officer may use as much force as he reasonably believes necessary, short of deadly force, to effect a lawful arrest. In the interests of showing that the force is necessary, the officer must state his purpose to arrest the person, unless he believes that the purpose is already known or cannot be made known, for example in the case where making the purpose known would frustrate the arrest (Model Penal Code, sec. 3.07; Restatement of Torts, 2d ed., sec. 128). An officer may also use necessary force to prevent a person from escaping from custody (LaFave and Scott, sec. 5.10). A private person, like a law enforcement officer, may use force that he reasonably believes to be necessary short of deadly force to effect a lawful arrest, and must state his purpose under similar circumstances; citizen's arrests of this type are quite unusual.

If an officer or other person uses more force to effect the arrest than he can reasonably believe necessary or proportional in the circumstances, the justification lapses, and the arresting person may be liable for criminal charges or for damages in tort for injuries due to "so much of the force as is excessive" (Restatement of Torts, 2d ed., secs. 132–133). Such cases are the ones that typically give rise to charges of "police brutality." In addition, if the actor is a public official the use of excessive force will be an "unreasonable seizure" of the person within the meaning of the Fourth Amendment to the U.S. Constitution. The test whether the force was excessive is an objective one, although, as the U.S. Supreme Court stated in the leading case, "[t]he calculus of reasonableness must embody allowance for the fact that police officers are often forced to make split-second judgments—in circumstances that are tense, uncertain, and rapidly evolving—about the amount of force that is necessary in a particular situation" (Graham v. Connor, 490 U.S. 386, 396–397 (1989)).

Police may also use reasonable force to effect a temporary stop, short of an arrest. In connection with such a stop, police are permitted to pat down the suspect for their own safety, to determine whether he has a weapon. They may also use force to detain the suspect; for example, police sometimes draw their weapons to ensure that there is no resistance, which has been held permissible at least where a serious crime is suspected (People v. Robinson, 68 NY2d 843 (1986)).

International law standards for the lawful use of force are derived directly from the principles of necessity and proportionality that underlie the justification. The United Nations Code of Conduct for Law Enforcement Officials (UN Code of Conduct) provides in Article 3, "Law enforcement officials may use force only when strictly necessary and to the extent required for the performance of their duty."