http://wiki.answers.com/Q/What_is_the_definition_of_being_detained_by_a_police_officer
What is the definition of being detained by a police officer?
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When a police officer wishes to question you, his actions fall under one of three areas: Contact, Detention, or Arrest.
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A Contact with you must be consensual. A police officer has not yet formulated enough suspicion of any wrong-doing to elevate this beyond a mere, "May I ask you a few questions?" You may be questioned, but you have the right to refuse to answer, and the right to walk away from a Contact.
An example of a Contact: A police officer walking his beat sees you and does not recognize you from the area. He may be curious as to why you are present, especially if it is a time of day when no one is usually about. However, you have done nothing to arouse his suspicion, so to satisfy his curiosity, he may Contact you and ask you some questions.
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A Detention is a non-consensual temporary denial of liberty. A police officer must have "reasonable suspicion" that
you are about to commit a crime
you are in the act of committing a crime, or
you have committed a crime
in order to Detain you. The officer has the authority to temporarily deny you the ability to leave while he investigates his suspicion. You may still refuse to answer any questions, but you have no right to leave. The officer must use a reasonable amount of time to investigate his suspicions until the detention elevates to the level of "probable cause" to arrest you. If the officer fails to determine there is probable cause for an Arrest, he must release you in a reasonable amount of time. The courts have determined that what is a reasonable amount of time is relative to the criminal activity being investigated. If you attempt to leave a detention without the permission of the police officer, you may be subject to Arrest. During a Detention, absent certain circumstances, a police officer may not move you to another location or the Detention becomes a de facto Arrest.
An example of a Detention: A police officer walking his beat sees you and does not recognize you from the area. He observes you for several minutes as you walk back and forth in front of a liquor store that is just about to close. You are wearing a red ballcap and the officer has taken two liquor store robbery reports this month about a person wearing a red ballcap entering the store just before closing time. You appear agitated and nervous, looking up and down the street. A police cruiser drives by and you duck into an alcove, then reemerge when the cruiser leaves. The officer determines that your actions are consistent enough with those of a robbery suspect that he believes he has reasonable suspicion to Detain you and investigate whether you are about to rob this liquor store.
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An Arrest occurs when the officer has determined that a crime has occurred and that there is "probable cause" to believe you committed the crime. An Arrest is non-consensual seizure of your person. Probable cause has sometimes been defined as "more likely than not," so the threshold is fairly low - the officer does not have to have sufficient evidence to prove your guilt, only that you are likely to be responsible based on objective evidence, such as someone identifying you, or physical evidence, or an admission. During an Arrest, you are still not required to answer any questions and you are not free to leave. You will be taken to jail and/or magistrate after you are Arrested.
An example of an Arrest: A police officer walking his beat hears an alarm start ringing from a local liquor store. He sees you run out of the store wearing a red ballcap and carrying a pistol in one hand and a handful of money in the other. The officer knows the clerk in the store on sight, and doesn't recognize you. The officer has taken two liquor store robbery reports this month about an armed person wearing a red ballcap entering the store just before closing time. Right after you run out, the clerk runs out, points at you and yells, "Help! I've been robbed!" The officer Arrests you because he has "probable cause" (based on his observation of your dress, your actions, and the clerk's words, it is more likely than not you just committed a robbery) to believe you have just committed an armed robbery.
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