Which legal concept requires that a police officer observe a suspect committing a crime?

The legal concept that requires a police officer to observe a suspect committing a crime is referred to as probable cause. Probable cause is a standard used in criminal law that ensures there is a reasonable basis for believing that a crime has been committed or that a specific individual has committed a crime. This is vital because it justifies law enforcement actions, such as arrests and searches without a warrant, under the Fourth Amendment.

When an officer directly observes a crime being committed, this creates an immediate and legally sound basis for action, aligning with the essence of probable cause. It is a more robust standard than reasonable suspicion, which only requires a minimal level of objective justification to initiate investigative actions, but does not permit arrests or searches.

In contrast, exigent circumstances refer to situations where law enforcement can act quickly without a warrant due to an urgent need to prevent harm, destruction of evidence, or escape of a suspect. An affidavit, on the other hand, is a written statement made under oath, often used in the context of obtaining a warrant but does not directly pertain to the observation of a crime. These distinctions highlight why probable cause is the appropriate legal standard in this context.