What must officers establish to conduct a search without a warrant?

To conduct a search without a warrant, officers must establish probable cause indicating involvement in a crime. Probable cause refers to a reasonable belief, based on facts and evidence, that a crime has been, is being, or will be committed. This standard is higher than mere suspicion and requires a factual basis for believing that a search would uncover evidence of criminal activity.

In practice, probable cause often arises from observable facts, reliable informant tips, or other evidence that leads law enforcement officers to believe that a search would be justified. This standard balances the need for effective law enforcement with the Fourth Amendment's protection against unreasonable searches and seizures.

Other options provided do not meet the threshold required for warrantless searches. For instance, random suspicion does not provide any factual basis and is insufficient to justify a search. Reasonable suspicion, while useful for brief stops and detentions (such as stop-and-frisk scenarios), is not enough to warrant a full search. Similarly, while testimony from a witness can contribute to a law enforcement officer's knowledge of a situation, it must still lead to a probable cause determination to justify a warrantless search.