So the Arizona immigration law does not allow the police officer to have contact with the person unless the contact is lawful. This means if even the briefest detention is involved, the police officer must have reasonable suspicion that some crime has been or is being committed. Absent that, the officer is not permitted to stop the person.
Now, why do I say the Arizona law is more restrictive of police than is federal law? Well, the Supreme Court has held that one common rationale for a permissible Terry stop is to ascertain the identity of the person who is detained. That is, federal law would probably permit an inquiry into citizenship as a part of establishing who the detainee is — again, as long as the officer had a good reason for detaining the person in the first place.

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