The criminal justice process typically begins when a police officer places a person under arrest. An "arrest" occurs when a person has been taken into police custody and is no longer free to leave or move about. The use of physical restraint or handcuffs is not necessary. 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 without the officer's use of any physical force. The key to an arrest is the exercise of police authority over a person, and that person's voluntary or involuntary submission.

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

The Police Officer Personally Observes a Crime

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

• While on street patrol, a police officer sees a purse snatching take place. The officer can apprehend and arrest the purse-snatcher, 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, and after administering a Breathalyzer test, sees that the driver's alcohol intoxication level is more than twice the state's legal limit for safe operation of a vehicle. The police officer can arrest the driver for DUI/DWI.

The Police Officer Has "Probable Cause" to Arrest

When a police officer 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 liquor store, then sees a man who matches the suspect's exact description running down the street near the store. The officer detains and searches the man, finding a gun and a large amount of cash in his pockets. The officer can arrest the man, based on a probable cause belief that he committed a robbery.