It is legal in most states for private citizens to make a citizen's arrest for a felony if you have reasonable grounds to believe that the person you have detained is the perpetrator. Felonies include: a hit and run, arson, murder, rape and theft of property (depending on the property value). You do not have to have witnessed the felony taking place in order to arrest the perpetrator.
In some states, arrests are allowed for misdemeanors involving breaches of the peace such as public intoxication or street brawling. However, in order to arrest someone for a misdemeanor, you must have personally witnessed the breach.
It is not the job of any private citizen to make a citizen’s arrest, and you should not attempt to do so when it would be practical to just call the police.
However, you might wish to attempt a citizen’s arrest in order to prevent the risk of further harm to yourself or others. It is also permissible where there is a need to apprehend a fugitive. You should always inform the detained person that you are making a citizen’s arrest and explain why. This will prevent any suggestion from the perpetrator that they thought they were under attack, and is particularly relevant if they fight back and you both end up suffering injuries. You should not try to make a citizen’s arrest on someone who you think could possibly be a criminal. A mere suspicion is not a satisfactory reason to tackle a person. For example, if you see a strange person who appears to be surveying your neighbor's empty house, do not approach them; call the police instead.
It is permissible to use force to affect an arrest, but the use of force must be reasonable. Whether your actions are deemed reasonable will be judged on a case-by-case basis. You can only use such force as is necessary to detain the person and prevent further injury, or to stop them from fleeing the scene. For example, if you weigh 130 pounds and detain a suspect with a similar frame by sitting on them, this might be considered reasonable. However, if you weigh 300 pounds and take similar action, it could be seen as an unreasonable force that is likely to cause injury to the suspect.
If you try to use force and misjudge the strength of the person whom you are seeking to apprehend, you could end up being physically hurt. And if the suspect turns out to be armed, you could place yourself and innocent bystanders at risk of serious harm. Trying to disarm a suspect could exacerbate an already bad situation, and is not recommended by law enforcement.
You are not permitted to beat the suspect in anger or to aggressively manhandle them, regardless of the fact that you may have witnessed them commit a heinous crime. This is vigilante behavior, which is not protected under the law. In addition, although you may be legally entitled to carry a weapon, this does not mean that you are automatically entitled to use it to detain a felon.
If they are unarmed and your response is deemed to be the use of unreasonable force, you will face serious criminal charges, particularly if you have used deadly force. The rules of each state will differ, but in most situations, you should not use deadly force to apprehend a suspect unless you or another victim is under attack. In such situations, you may be able to claim self-defense.
Crime control is best left to trained law enforcement professionals. You should consider the rules of your state before you attempt to make a citizen’s arrest, as there are many risks associated with doing so. Private citizens are not afforded the same protections as police officers, who in most cases are allowed to make a mistake of fact and detain anyone on reasonable suspicion.
If you are in doubt as to whether a crime has been committed, you should avoid trying to make a citizen’s arrest. It is quite possible that you are mistaken in your belief and, unfortunately, eyewitnesses are notorious for being mistaken. You could be witnessing a couple of friends playing around or even a documentary team filming a scene.
In general, if there were no reasonable grounds for you to arrest the suspect, you could face the serious charges of false imprisonment or kidnapping. If the suspect is hurt, you may also be sued for negligence or assault and battery, as well as violating the suspect’s civil rights.
Some states allow you to transport the suspect to law enforcement yourself; however, for the safety of yourself and others, it is preferable to call law enforcement and let them take over. If you are physically holding on to the suspect, ask a bystander to contact the police and ask any witnesses to stay with you until the police arrive. The police will take over the arrest from you, so be prepared to relate every detail of what led up to the detainment of the suspect.