A tribal police officer can temporarily detain a non-Native American person traveling through a reservation for potential violation of state or federal law, the U.S. Supreme Court held June 1 in United States v. Cooley.
Joshua Cooley was parked by a road in the Crow Reservation in Montana.  He was approached by a Crow police officer, who saw that Cooley appeared to be intoxicated.  Subsequently, the tribal officer found drugs and guns in Cooley’s truck.   
The officer called county and tribal officers for assistance.  Cooley was arrested.
Cooley was charged with federal drug and gun offenses.
He moved to suppress the drug evidence the tribal officer had seized.  The district court granted the motion on grounds that a tribal officer lacks authority to investigate nonapparent violations of state or federal law by a non-Native American on a public road which crosses a reservation.
The Ninth Circuit affirmed.
The Supreme Court reversed, in a unanimous opinion by Justice Breyer.
Native American tribes are “distinct, independent political communities exercising sovereign authority,” the Court said.  “Due to their incorporation into the United States, however, the sovereignty that the Indian tribes retain is of a unique and limited character.”
Although Native American tribes have authority over some matters, “[t]ribes … lack inherent sovereign power to exercise criminal jurisdiction over non-Indians,” the Court said.  But “[i]n all cases, tribal authority remains subject to the plenary authority of Congress.”
“Here, no treaty or statute has explicitly divested Indian tribes of the policing authority at issue,” the Court said. Thus, “[w]e turn to precedent to determine whether a tribe has retained inherent sovereign authority to exercise that power.”
The Court had previously held that tribes “retain inherent power to exercise civil authority over the conduct of non-Indians on fee lands within its reservation when that conduct threatens or has some direct effect on the political integrity, the economic security, or the health or welfare of the tribe,” the Court said.
“The phrase speaks of the protection of the ‘health or welfare of the tribe,’” the Court said.  “To deny a tribal police officer authority to search and detain for a reasonable time any person he or she believes may commit or has committed a crime would make it difficult for tribes to protect themselves against ongoing threats.”
“Such threats may be posed by, for instance, non-Indian drunk drivers, transporters of contraband, or other criminal offenders operating on roads within the boundaries of a tribal reservation,” the Court said.
Prior cases denying tribal jurisdiction over non-Native Americans have emphasized that application of tribal law to non-members of a tribe may be unjust since non-tribal members had no say in creating the laws that would be applied to them.
But the search and detention of Cooley did not subject Cooley to tribal law, the Court said.  Instead, Cooley is charged under the same federal or state law that would apply to any individual whether inside or outside of a tribal reservation.