Here is the opinion. An excerpt:

This case presents the question whether the State of Washington may exercise criminal jurisdiction over members of the Confederated Tribes and Bands of the Yakama Nation who commit crimes on reservation land. To answer that question, we must interpret a 2014 Washington State Proclamation that retroceded—that is, gave back—“in part,” civil and criminal jurisdiction over the Yakama Nation to the United States, but retained criminal jurisdiction over matters “involving non-Indian defendants and non-Indian victims.” If “and,” as used in that sentence, is conjunctive, then the State retained jurisdiction only over criminal cases in which no party—suspects or victims—is an Indian. If, by contrast, “and” is disjunctive and should be read as “or,” then the State retained jurisdiction if any party is a non-Indian. We conclude, based on the entire context of the Proclamation, that “and” is disjunctive and must be read as “or.” We therefore affirm the district court.

Briefs here. Oral argument video here.