The respondent in this case, a non-Indian, was detained and searched by a tribal police officer on a public highway that traversed the Crow Reservation in Montana. The officer discovered the respondent in his truck on the roadside, noticed that he had watery, bloodshot eyes and saw two semiautomatic rifles in his front seat. The officer detained the defendant and seized the guns and the drugs that he later discovered in the respondent’s truck. The respondent was federally indicted for drug and gun offenses. The trial court suppressed the drug evidence on the basis that the tribal officer lacked the authority to investigate nonapparent violations of law by a non-Indian on a public right of way on the reservation. The Ninth Circuit affirmed.

A unanimous Supreme Court vacated the Ninth Circuit’s judgment.

The Court, in an opinion authored by Justice Breyer, held that the officer was authorized to detain and search the respondent based on the tribe’s inherent sovereign authority to address conduct that threatens or has some direct effect on the health or welfare of the tribe. This authority is an exception to the general proposition that the inherent sovereign powers of an Indian tribe do not extend to the activities of nonmembers. The Court explained that to deny a tribal police officer the authority to detain and search a person the officer believes may commit or has committed a crime would make it difficult for tribes to protect themselves against ongoing threats. Earlier cases denying tribal jurisdiction over the activities of non-Indians on a reservation relied in part on the fact that applying full tribal jurisdiction would subject non-Indians to tribal law they had no role in creating. The tribal officer’s detention and search of the respondent, in contrast, did not subject him to tribal law, but instead to state and federal laws that apply whether the person is outside the reservation or on a state or federal highway within it. Finally, the Court rejected the argument that existing federal statutes granting tribes limited authority to enforce federal law divested tribes of this sovereign authority.

Justice Alito concurred, stating that he joined the opinion of the Court with the understanding that it only held the following:  On a public right-of-way that traverses an Indian reservation and is primarily patrolled by tribal police, a tribal officer may (a) stop a non-Indian motorist based on reasonable suspicion of a violation of state or federal law; (b) search to the extent necessary to protect the officer and others; and (c) if the officer has probable cause, detain the motorist for the period of time reasonably necessary for a non-tribal officer to arrive.