In what scenario can police conduct a reasonable search without a warrant under the Fourth Amendment?

Police can conduct a reasonable search without a warrant under the Fourth Amendment in situations where there is reasonable suspicion of criminal activity. This standard is lower than probable cause, which is necessary for obtaining a warrant, yet it still requires specific and articulable facts that suggest a crime may be occurring or is about to occur. Reasonable suspicion allows law enforcement officers to take immediate action to ensure public safety or preserve evidence, especially in situations where a delay could compromise their investigation or endanger individuals.

In contrast, while suspicious behavior and a fleeing suspect may provide context or contribute to a legal justification for an encounter, they do not independently establish reasonable suspicion. Similarly, prior knowledge about an individual might inform an officer's intuition or awareness but does not constitute reasonable suspicion on its own. Thus, the principle behind this answer emphasizes the necessity for officers to have specific facts pointing to criminal activity in order to justify a search without a warrant.