What must exist for a police officer to arrest without a warrant?

To arrest without a warrant, a police officer must have probable cause. This means that the officer has a reasonable belief, based on facts and circumstances, that a crime has been, is being, or will be committed. Probable cause is a legal standard that is foundational to the authority of police officers to act without a warrant; it is essential to protect individuals from unreasonable searches and seizures under the law.

In contrast, the requirement for reasonable grounds to believe that a name or address is false, while it might come into play in certain investigative contexts, does not suffice on its own to justify a warrantless arrest. The existence of an immediate threat to public safety might prompt an officer's action in some scenarios, but it too does not replace the need for probable cause. Public permission is not a legal requirement for an officer to carry out an arrest, as law enforcement officers operate under statutes and legal frameworks that dictate their powers and responsibilities. Therefore, the requirement of probable cause is crucial for ensuring that arrests are made lawfully and with justification.