When can the police arrest someone?

Generally, an "arrest" takes place when a person has been taken into police custody and is no longer free to leave or move around. In this sense, the use of physical restraint or handcuffs is not necessary for a person to be considered under arrest. Rather, an arrest can be complete when a police officer simply tells a crime suspect that he or she is "under arrest", and the suspect submits – voluntarily or involuntarily – to the authority of the police officer. 

A police officer may usually arrest a person in the following circumstances:

The police officer claims to have personally observed a crime

If a police officer observes someone commit a crime, the officer may arrest that individual. For example:

  • While on street patrol, a police officer witnesses a robbery take place. The officer can apprehend and arrest the robber, based on the officer's personal observation of a theft/larceny or robbery.                                                                                                            
  • A police officer pulls over a vehicle that is being driven erratically. After conducting a Field Sobriety Test and/or administering a Breathalyzer test, and concluding that the driver is legally intoxicated, the police officer can arrest the driver for DUI/DWI.

The police officer has “probable cause” to arrest a person

When a police officer has not observed a crime, but has a reasonable belief, based on facts and circumstances, that a person has committed or is about to commit a crime, the officer may arrest that person. This belief, known as "probable cause," may arise from any number of different facts and circumstances. For example:

  • A police officer receives a report of an armed robbery that has just occurred at a local bank, then sees a man who matches the suspect's exact description driving away from the scene of the crime. The officer can then pursue and detain the man, and if enough facts exist to indicate probable cause that the man committed the robbery – e.g. if the man is in possession of a gun and large amounts of cash – arrest the man for robbery.

An Arrest Warrant Has Been Issued

When a police officer has obtained a valid warrant to arrest a person, the arrest is lawful. An arrest warrant is a legal document issued by a judge or magistrate, often obtained after a police officer has submitted a sworn statement that sets out the factual basis for the arrest. Typically, when issued, an arrest warrant:

  • Identifies the nature of the crime(s) committed;
  • Identifies the individual(s) suspected of committing the crime;
  • Delineates, with specificity, the location(s) where the individual may be found; and
  • Gives a police officer permission to arrest the person(s) identified in the warrant.

How to Challenge An Unlawful Arrest

At all stages of the criminal process, including arrest, police officers have a duty to protect a person’s constitutional rights, whether that person is a citizen, non-citizen or so-called illegal immigrant – yes, the United States Constitution has generally been interpreted to apply to illegal immigrants, too. Some of these rights include a person’s right to remain silent and the right to be free from unreasonable searches. If these rights are violated, a court has discretion to deem the arrest unlawful and order that the case against the arrestee dismissed, or otherwise that certain evidence obtained during the unlawful arrest be thrown out.  

Still, even if you believe the officer has no grounds to arrest you, it is not recommended that you argue with or resist the police. You have no legal right to argue about why you are being arrested or about your guilt or innocence at the time of the arrest. Arguing or resisting simply gives the police a reason to bring additional criminal charges against you; and it may make it harder for you to get out of jail on bail if you are charged. Leave any battle involving the legality of your arrest in the courtroom, rather than on the street.