Final answer:
Probable cause is a legal requirement allowing officers to arrest or search, based on either direct observations or credible information. This standard is established by the Fourth Amendment to prevent unreasonable searches and seizures. Circumstances like vehicle searches or Terry stops require less evidence than a formal warrant.
Step-by-step explanation:
Probable cause is a legal standard in law enforcement that allows police officers to make an arrest, obtain a warrant, or conduct a search. An officer's direct observations or reasonably reliable information can create probable cause to believe that a person has committed a crime. The concept is crucial in protecting individuals' rights against unreasonable searches and seizures, as stated in the Fourth Amendment.
For example, in the scenario where police apprehend two individuals suspected of committing an armed robbery, despite lacking direct evidence, the possession of unlawful weapons and circumstantial evidence can contribute to establishing probable cause for arrest. Under the Terry v. Ohio decision, an officer can stop and frisk individuals if there is reasonable suspicion of criminal activity and concern for public safety.
When obtaining a search warrant, police must convince a judge that there is probable cause to believe that evidence of a crime will be found, which is a lower standard of proof than is required for a conviction. Moreover, specific circumstances like searching a car's passenger compartment or border searches don't always require a warrant due to lesser expectations of privacy.