I was looking at the rules governing a Motion to Suppress Evidence in an immigration court, such as a non-voluntary statement, and the rules governing the Fourth Amendment and the Exclusionary Rule as they pertain to the immigration proceedings, and much to my surprise, the courts, even the Ninth Circuit, has already given broad powers to immigration officers to interrogate anyone suspected of being an alien.
It is only a small step to giving the same powers to a state law enforcement officer. Interesting con law issue, but much closer than I would have suspected initially.
"Any immigration officer has the power, without warrant, to interrogate any alien or person believed to be an alien as to his or her right to be or remain in the United States." INA § 287(a)(1); 8 C.F.R. § 1287.5; Cervantes v. United States, 263 F.2d 800 (9th Cir. 1959); Matter of Pang, 11 I&N Dec. 213 (BIA 1965).
"There is no requirement that the officer must have probable cause for such an inquiry." Matter of Perez-Lopez, 14 I&N Dec. 79 (BIA 1972).