the legality of questioning someone's immigration status was in the court decision regardless of the circumstances..
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stop interpreting the law. "Because Mena’s initial detention was lawful and the NinthCircuit didnot hold that the detention was prolonged by thequestioning,"

"officers executing a search warrantfor contraband have the authority “to detain the occupants of thepremises while a proper search is conducted.”
meaning they couldn't have detained them withpout a warrant.
and only "Because Mena’s initial detention waslawful and the Ninth Circuit did not hold that the detention wasprolonged by the questioning there was no additional seizure within the meaning of the Fourth Amendment, and, therefore, no additional Fourth Amendment justification for inquiring about Mena’s immigration status was required."