State police officers can pursue members of the Navajo Nation onto the reservation and investigate crimes committed off the reservation, the New Mexico Supreme Court ruled on Tuesday.

David Harrison, a tribal member, was suspected of speeding and driving under the influence on a state highway. He wasn't stopped by a state officer until he was already on the reservation.

The court ruled that the state officer had the authority to stop Harrison to determine, as an initial matter, his tribal status. But the court also said the officer had the authority to conduct an investigation to determine the extent of Harrison's offenses.

In this case, the officer conducted field sobriety tests, which Harrison failed. The court said the investigation did not infringe on the Navajo Nation's sovereignty because the tribe has not enacted its own laws regarding such tests.

The court noted that Harrison was not arrested at the scene. The officer later obtained an arrest warrant by following Navajo Nation laws.

"We conclude that state officers have the authority to enter Indian country to investigate off-reservation crimes committed in their presence by Indians, so long as the investigation does not infringe on tribal sovereignty by circumventing or contravening a governing tribal procedure," the court said in the opinion. "The traffic stop in this case, which included the administration of field sobriety tests, did not circumvent or contravene the Navajo Nation Code and, therefore, did not infringe on the sovereignty of the Navajo Nation."

Supreme Court Decision:
New Mexico v. Harrison (June 8, 2010)

Appeals Court Decision:
New Mexico v. Harrison (June 24, 2008)