The most common reason for a person to be stopped by the police are:
Traffic violations - A driver pulled over for violating the rules of the road;
Suspicion of Criminal Activity - The police have reason to believe that the person they are stopping is engaged in criminal activity;
Criminal Conduct - The police observed the person commit a criminal offense, or reasonably believe that the person has committed a criminal offense; and
Arrest Warrants - The police are enforcing a warrant for the person's arrest.
After being stopped and detained by the police, a person will typically be questioned.
Even without arresting a person, the police may stop the person and ask questions.
Upon seeing suspicious activity, the police may perform what is called a Terry Stop.1: without making an arrest, the police may temporarily detain people to request that they identify themselves and to question them about the suspicious activity. The scope of a Terry Stop is limited to investigation of the specific suspicious activity, and if the police detain people to question them about additional matters, the stop may turn into an arrest.
During a Terry Stop, in order to ensure their own safety, the police may perform a pat-down or weapons frisk on the outside of a person's clothes. During this frisk, if the police feel something that they reasonably believe may be a weapon, they may remove the item from the suspect's clothing for further examination. However, absent unusual circumstances the police are not entitled to remove items from person's pockets that do not appear to be weapons, even if they believe that the items are contraband.2
Many people think of an arrest as being a formal declaration by the police, "You are under arrest," followed by the reading of the person's Miranda rights: As seen on TV: "You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to an attorney. If you cannot afford an attorney, one will be appointed to represent you."
The actual law is more complicated than most TV shows suggest. An arrest occurs when a person no longer reasonably expects that he is free to leave.
A Terry Stop is not an arrest, even though the person can't leave during the investigatory questioning, as the detention is of short duration and is limited in its scope. A Terry Stop may involve little more than a short series of questions, such as, "What is your name? Where do you live? Why are you here?"
However, if a person is not allowed to leave the scene for an extended period of time, the person may be considered to be "under arrest," even though those words are never used.
If a person is handcuffed, is locked in the back of a police car, or is otherwise restrained from leaving, the person will normally be considered to be "under arrest."
While a Terry Stop can be made upon reasonable suspicion that a person may have been engaged in criminal activity, an arrest requires probable cause that a suspect committed a criminal offense.
If the police ask for permission to search you or your property, you may say "no".
The only reason a police officer wants to perform a search is to find evidence of criminal activity, and the fact that the officer is asking for permission to search reflects the officer's expectation that the search will produce contraband or evidence of a crime. If the police officer has the legal authority to perform the search, the officer will continue with a search whether or not you agree. However, if the officer does not have the legal authority to perform a search, your consent gives the officer that authority. By giving valid consent, you lose your ability to later challenge the constitutionality of the search or the use of evidence obtained through the search.
During an investigative stop, including a traffic stop, a police officer may ask for permission to search you or your car. If you give the police officer permission to search, the search may proceed even though the officer otherwise had no legal authority to do so. Even if you're certain that a police officer won't find anything illegal in your car, you may be in for a surprise. Some people don't know, or forget, that they have an "open" bottle of liquor in the car -- a bottle with the seal broken, whether or not the cap is off. Sometimes people have knives, weapons or other objects in their vehicles can be classified as illegal concealed weapons. Sometimes, people forget that they have contraband in their cars, such as illegal drugs, or find to their chagrin that their teenaged child dropped a marijuana cigarette in the car. Unless you are the only person with access to the interior of your car you can't be certain what the police will find, and even then you may find that your memory has failed you.
The police have no obligation to formally announce the arrest when it occurs, nor are they required to read a suspect his Miranda Rights. In most cases, at some point the police will inform a suspect that he has been arrested. However, many defendants never receive their Miranda Rights, which relate to the validity of police questioning of suspects who are in custody, and not to the arrest itself.
For most misdemeanor offenses, a police officer can only make a warrantless arrest of a suspect if the offense was committed in the officer's presence. Officers can arrest people for felonies based upon witness statements that create probable cause for an arrest, or where a warrant for the person's arrest has been issued.
If a person is arrested illegally and is searched or questioned by the police, evidence gained through the search or questioning may be declared inadmissible in subsequent criminal court proceedings. However, there are circumstances under which that evidence may be admitted into court despite the illegality of the arrest. Further, if a person has outstanding warrants for other charges, the person may be detained on those charges even though the initial arrest was illegal.
It is important to note that an "illegal arrest" does not mean that a person can't be charged with a crime. The unlawful nature of the arrest may affect the admissibility of evidence obtained as a consequence of the arrest, but the underlying criminal conduct may still be prosecuted using other, admissible evidence.
The police have the authority to perform a search of a suspect and his immediate surroundings, "incident" to the arrest of the suspect. If the police arrest a person who was driving a car, they ordinarily get the authority to search the entire passenger compartment of the car -- and will usually also be able to search passengers for weapons. If the car is impounded, the police may perform an "inventory search" of the entire car, including the contents of the trunk.
1. The Terry stop is named after the case that defined this type of investigative stop by the police, Terry v. Ohio, 392 U.S. 1, 88 S.Ct. 1868, 20 L.Ed.2d 889 (1968).
2. On occasion an item of contraband might be identifiable based upon how it feels through a person's clothing, in which case it might be possible for the police to investigate further under the "plain feel" exception to the requirement for a search warrant.