A police officer for the Crow Tribe approached a driver who had stopped on a portion of a public highway within the Crow Reservation. The officer observed the driver appeared not to be native and had watery, bloodshot eyes, and guns on the front seat. Without asking for identification that would resolve the driver’s status as a native, the officer ordered the driver out of the car and conducted a search, which uncovered illegal drugs. The driver was indicted for gun and drug offenses. The district court granted a motion to suppress the drug evidence and the Ninth Circuit affirmed, holding that a tribal police officer lacked authority to investigate non-apparent violations of state or federal law by a non-Indian on a public right-of-way, and that tribal officers could only stop a non-Indian suspect for a reasonable time if the officer first tries to determine if the non-Indian is an Indian, and if not, it is “apparent” that the non-Indian was violating state or federal law.

The Court, in a unanimous opinion by Justice Breyer, reversed, holding that while tribal sovereign authority did not normally provide criminal jurisdiction over non-Indians on reservation land, this case “fit like a glove” under the exception stated in Montana v. United States, 450 U.S. 544 (1981), when the non-Indian’s conduct “threatens or has some direct effect on the political integrity, the economic security, or the health or welfare of the tribe.” There was no requirement that the officer first ask about citizenship, and the tribal officer was not restricted in detaining someone only if was already “apparent” that a crime had been committed. The majority found no congressional abrogation of the tribe’s authority to police the public roads in its reservation over Indians and non-Indians alike. Justice Alito submitted a short concurrence stating his limited view of the holding.

A link to the opinion in United States v. Cooley is here: https://www.supremecourt.gov/opinions/20pdf/19-1414_8m58.pdf