All states authorize private citizens to make arrests. For example, a car owner may arrest a teenager trying to break into her car, and a store security guard can stop and detain a shoplifter. Citizens who arrest others sometimes do good, but other times, it can result in a heap of trouble.
In order to encourage citizens to leave arrests to the professionals, laws in almost all states afford less protection to private citizens who make mistakes during the arrest process than they do to police officers.
Most states authorize private citizens to make arrests if the suspect:
While state laws vary, many states require the citizen to turn over the suspect to the police without delay. (The citizen cannot take justice into his or her own hands.)
It's sometimes considered a citizen arrest even when a private person reports a misdemeanor offense but lets the police handle the actual arrest. Say a citizen witnesses a shoplifter and calls the police. When the police arrive, the officer arrests the shoplifter. The arrest may be valid under what's called the "delegated citizen's arrest."
Why do we care who does the actual arresting? Because, generally, neither private citizens nor police officers can make warrantless arrests for misdemeanors they don't personally witness. A citizen who witnesses a misdemeanor has arrest authority. A police officer who witnesses a misdemeanor has arrest authority. But in the case of the citizen witnessing the offense and the officer making the arrest, we have a gap in arrest authority—the citizen has it, the officer does not.
To fill this gap, some states allow a delegated citizen's arrest, which transfers the citizen's arrest authority to the officer. So in the case of the shoplifter, the citizen who witnessed the offense delegates her arrest authority to the officer—making the officer's arrest valid.
Police officers have much more leeway in conducting arrests. For example, if they arrest someone they reasonably but mistakenly believe to have committed a felony, they're probably in the clear. But a private citizen who arrests someone for an apparent—but not actual—felony might be liable to the arrestee for a tort like false imprisonment.
Example 1. While eating lunch in the park, Ella Mentry thinks she has overheard two people talking about a plan to rob Haro's Jewelry Store. As the two people walk away, Ella realizes that one of the individuals is her next-door neighbor. About an hour later, Ella sees a crowd and two police officers gathered in front of Haro's. She immediately rushes to the neighbor's house and places him under arrest for robbery. It turns out, however, that there was no robbery—the police and crowd had gathered for a diamond-cutting demonstration. Ella is civilly liable to her neighbor and may have to pay damages to compensate for the time, trouble, and distress of the improper arrest.
Example 2. Same case. Assume that after overhearing her neighbor talking about what she thought was a plan to rob Haro's, Ella tells Officer Chang what she heard. About an hour later, Officer Chang sees a large crowd gathered in front of Haro's and Ella's neighbor running away from the store. He runs after and arrests the neighbor. Again, it turns out that Haro's wasn't robbed. Rather, the neighbor was late for a nearby appointment. Because Officer Chang had probable cause to believe the neighbor was involved in the robbery, he is immune from liability in a subsequent lawsuit for wrongful arrest.
Private citizens roll the dice by trying to arrest others. Not only can they expose themselves to grave danger but also to civil liability and criminal prosecution. The legal ramifications are heightened when private citizens use deadly force to make arrests. Courts are rightly fearful that any encouragement of this kind of behavior will lead to armed vigilantes roaming the streets. That's why a private citizen's use of deadly force in making an arrest isn't justified unless that force was necessary to protect him or herself or others from extreme harm.
Almost always, the best course of action is to get the police involved. Private citizens should turn their information over to the cops rather than personally make arrests. If they end up making an arrest, they must contact the police as soon as possible.
If you have questions about the law or your rights, contact an attorney. An attorney who works in civil litigation can help you understand how to bring or defend a lawsuit brought in civil court. If criminal charges are involved, speak to a criminal defense attorney.