Ybarra v. Illinois

Search warrants do not authorize frisks of persons who, at the commencement of the search, are on the premises subject to a search warrant. A person’s proximity to others independently suspected of criminal activity does not, without more, justify a frisk.

The officer’s justification for the search of the defendant rested on a state statute permitting an officer, in the execution of a search warrant, to reasonably detain and search any person on the premises to either protect himself from attack, or to prevent the disposal or concealment of anything particularly described in the warrant. This statute offends the Fourth Amendment where:

1) No probable cause existed at the time the search warrant was issued for the authorities to believe that any person found in the tavern other than the employee would be violating the law;

2) There was no probable cause to search the defendant at the time the warrant was executed;

3) The customers in the tavern maintained their own protection against an unreasonable search or seizure which was separate and distinct from that possessed by the proprietor of the tavern or by the employee, and;

4) The initial frisk of the customer was not supported by a reasonable suspicion that he was armed and dangerous.