The authority to prosecute non-member Indians for minor crimes had been taken from tribes in the Supreme Court decision of 1992 known as Duro, on the precedent of an earlier case, known as Oliphant, that ruled tribes can lose sovereignty if the Supreme Court finds its exercise "inconsistent with the tribe's dependent status."
When the Duro decision opened up a jurisdictional gap that made it impossible to prosecute non-member Indian miscreants on reservations, Congress, acting on the Duro court's own advice to fashion a remedy if needed, passed the so-called "Duro fix," restoring tribal authority over non-member Indians. Congress thereby recognized and affirmed the inherent power of tribes to prosecute non-member Indians for minor crimes committed on the host reservations.
For more than 10 years, the "Duro fix" worked well in protecting tribal communities from nonmember minor crime.
Enter Billy Jo Lara. A Turtle Mountain Chippewa tribal member, Lara married a Spirit Lake tribal member and moved to that North Dakota reservation. After repeated offenses, he pleaded guilty in tribal court to infractions of the tribal code stemming from his violation of a tribal expulsion order. The penalties levied against him included a 90-day jail sentence for striking a tribal officer. Then federal prosecutors in North Dakota brought charges of assault on a federal officer, a BIA employee, during the same arrest.
Lara had already pleaded guilty in the tribal case, and all the elements in the federal case against him were the same. Under any ordinary scenario, that would put him in "double jeopardy," a violation of the Fifth Amendment to the U.S. Constitution, which protects citizens from being tried twice over for the same alleged offenses.
But what seemed to remove the Lara case from the realm of double jeopardy was the presence of separate sovereigns. One sovereign, the tribe, was bringing one set of charges, and another sovereign, the federal government, was bringing the graver charge, both on the same case elements. In the same way, different states, acting as separate sovereigns, will often bring charges for the same crimes committed within their separate jurisdictions.
This interpretation depends on the validity of congressional intent to restore inherent tribal power that had been set aside by the Supreme Court in Duro. Lara argued, however, that Congress delegated federal sovereign power to the tribe for prosecution of non-member Indians. If the Supreme Court finds that Congress did delegate its own federal powers, rather than restoring tribal powers that exist (or not) separate from the federal government, the sovereigns in the case will not be considered separate and Lara may avoid the federal assault charge, having already been tried on the lesser tribal charges.