You're walking down the street when a police officer orders you to halt and begins asking you questions. You're pretty sure that you're not free to leave. Does that mean that you've been arrested, or are you simply being detained?
In general, if a reasonable person in the suspect's shoes wouldn't feel free to leave an encounter with the police, then there's been either a detention or an arrest. Determining which can be tough—and sometimes crucial.
Suppose, for instance, that an officer has reasonable suspicion to detain someone but not probable cause to arrest them. In the course of the encounter, the officer discovers incriminating evidence. In this situation, if the defense attorney persuades the court that, instead of merely detaining her, the officer arrested the suspect without probable cause, then the evidence may be inadmissible in court.
(For information about the level of suspicion police officers must have in order to detain or arrest, see What's the difference between an arrest and a detention or "stop and frisk"?)
Sometimes it's clear someone is under arrest—for instance, when the officer specifically says so and then handcuffs the person. But not all situations are that clear. Because it can mean the difference between incriminating evidence being admitted or not in a case, a judge may have to decide.
An officer's "brief and cursory" holding and questioning of someone is a detention. An example is a cop stopping someone who is behaving suspiciously in order to ask a few questions. The suspect isn't free to leave, but he also isn't under arrest, at least until the officer develops probable cause. Another common example is an officer pulling over a driver for some kind of traffic or equipment violation.
An arrest, on the other hand, involves the police taking someone into custody through a more significant restraint on movement. The quintessential example involves the use of handcuffs and an advisement that the suspect is under arrest. (See How do I know if I've been arrested?)
Investigatory stops (or "detentions") must be no longer than necessary and officers must investigate with the least intrusive means that are reasonably available. When an officer prolongs a detention beyond what is brief and cursory and broadens it, then the detention may turn into a de facto arrest—that is, an actual but not official arrest.
If a reasonable person in the suspect's position would have considered the police's behavior to constitute the kind of restraint that's typical of formal arrest, then an arrest has occurred. Some courts phrase the issue as depending on whether, after brief questioning, a reasonable innocent person would have felt free to leave—if not, there's been an arrest. (Johnson v. Bay Area Rapid Transit Dist., 724 F.3d 1159 (9th Cir. 2013).)
Courts consider a variety of factors in determining whether a detention has ripened into an arrest, among them:
(U.S. v. Vargas, 369 F.3d 98 (2d Cir. 2004), In re Hoch, 82 A.3d 1167 (Vt. 2013).)
Although the extent to which officers restrain and intrude upon the suspect are key to the determination, there's no bright line indicating the point at which a detention becomes an arrest. For instance, the use of handcuffs doesn't automatically signal an arrest where there are concerns for officer or public safety.
In one case, officers handcuffed a suspect and placed him in the back of a squad car while they searched a house he had just visited. The appeals court held that their actions didn't turn the detention into an arrest because they needed to avoid an escape attempt and to take precautions against potential violence. The court also found that it made sense to take the suspect back to the house because they knew that the search they were about to begin could implicate him. (United States v. Bullock, 632 F.3d 1004 (7th Cir. 2011).)
If you have questions regarding a police encounter, talk to a criminal defense attorney. An attorney can help you understand the law and how it applies in your case.