Under what circumstance can a police officer arrest someone without a warrant?

A police officer can arrest someone without a warrant primarily when a crime is committed in their presence. This is grounded in the principle that immediate action is necessary to address criminal behavior as it occurs. The law allows officers to take decisive action to prevent further harm, gather evidence, or detain a suspect before they have a chance to escape or destroy evidence.

When a crime is observed directly by the officer, it provides clear evidence of wrongdoing, justifying the immediate arrest without needing a warrant. This capability is vital for maintaining public safety and order, allowing law enforcement to respond effectively to ongoing criminal activity.

The other circumstances mentioned do not inherently provide the right to arrest without a warrant. For instance, a tip-off could provide valuable information but doesn't constitute direct evidence of a crime occurring. A witness statement, while potentially helpful, does not give an officer enough legal basis to act immediately unless it is corroborated by what the officer can independently observe. Reasonable suspicion allows officers to stop and briefly detain a person for questioning but falls short of the probable cause needed for an arrest. Thus, the ability to arrest without a warrant is specifically tied to the officer witnessing a crime taking place firsthand.