Frederick County Board of Commissioners v. Santos

Issue: (1) Whether federal law preempts the brief detention of an alien by a local police officer, pursuant to a federal warrant, for the purpose of contacting Immigration and Customs Enforcement to determine if the alien should be taken into custody, when it is unknown whether the alien’s violation of federal immigration law was criminal or civil; and (2) whether the Fourth Amendment prohibits a brief investigative stop of an alien when the law enforcement officer reasonably suspects that the alien has committed a violation of federal immigration law, regardless of whether it is civil or criminal in nature.