The question here is whether an assault on a tribal officer can be prosecuted as an assault on a federal officer under the Major Crimes Act. The court concluded that whether the tribal cop is a federal cop must be proven beyond a reasonable doubt.
Here is the Court’s opinion in United States v. Danley.
Turtle Talk 
Does anyone have a copy of the federal government’s briefs on this case?
Yep. But I’m traveling. Later.
So what do you think? Are they automatically granted federal protection? Or is the officer required to have SLEC in order for this protection? Was he enforcing federal law? Is this really a major crime that should be prosecuted federally??