The job of police officers can be tough. They have to ferret out crimes and arrest dangerous criminals. The police, however, cannot just arrest on a whim any person suspected of committing a crime; they have rules and regulations to follow. Usually a lawful arrest requires an arrest warrant, but even if an arrest warrant is not required, probable cause must exist.
Elements of an Arrest
A legal arrest occurs if a police officer executes an arrest warrant bearing the suspect's identity, and the police officer arrests the person. A legal arrest also occurs when a police officer has probable cause to believe a person has committed a crime, and arrests the person. A person can tell the difference between an arrest and just a stop by the police by deciding whether he, or a reasonable person, would feel free to leave after being stopped by the police officer.
To obtain an arrest warrant, a police officer must have probable cause. The police officer prepares a written affidavit setting out the factual basis for probable cause. When a police officer knows of certain circumstances and facts that would be sufficient for a reasonable person to believe that a suspect has committed a crime, is committing a crime, or is about to commit a crime, he has probable cause.
With probable cause and his affidavit, the police officer goes to a neutral and detached magistrate. The magistrate determines if there is sufficient probable cause; an oath or affirmation by the requesting officer that the warrant's contents are accurate; a particular description of the person to be arrested; and a statement of when, where and how the warrant will be executed. The police officer finally executes the arrest according to the terms and scope of the arrest warrant.
Arrest in a Home
If a police officer plans to arrest a person within his own home, that police officer needs to obtain an arrest warrant. He also needs to have reason to believe the suspect is located within the home for the arrest to be lawful. People have an expectation of privacy in their own homes, even against the police. If the police were to enter a person's home to arrest a suspect without a warrant, that would only be lawful under an emergency situation. If the policeman had time to obtain a warrant before the arrest but did not obtain the warrant, that arrest would not be lawful.
Arrest of a Fleeing Suspect
Sometimes a suspect's behaviour can elevate a police officer's reasonable suspicion to the level of probable cause, prompting an arrest. If a police officer suspects that a person has been involved in a crime, he can question that person. If the person notices the police officer approaching and runs, this may increase the police officer's reasonable suspicion to probable cause for an arrest. At this time, the police may chase this person and arrest him.