Here is the opinion in United States v. Zepeda.

From the syllabus:

The en banc court affirmed a defendant’s convictions and sentence under the Indian Major Crimes Act, which authorizes federal jurisdiction over certain crimes committed by Indians in Indian country.

The en banc court held in order to prove Indian status under the IMCA, the government must prove that the defendant (1) has some quantum of Indian blood and (2) is a member of, or is affiliated with, a federally recognized tribe. The court held further that under the IMCA, a defendant must have been an Indian at the time of the charged conduct, and
that, under the second prong, a tribe’s federally recognized status is a question of law to be determined by the trial judge. Overruling United States v. Maggi, 598 F.3d 1073 (9th Cir.
2010), the en banc court held that the federal recognition requirement does not extend to the first prong of the Indian status test. The court held that the evidence at trial was sufficient to support the finding that the defendant was an Indian within the meaning of the IMCA at the time of his crimes.

The en banc court held that the defendant’s sentence was not unreasonable because it was mandated by 18 U.S.C. § 924(c), which required the district court to impose consecutive mandatory minimum sentences on the defendant’s convictions for use of a firearm during a crime of violence.

The en banc court agreed with the three-judge panel’s reasons for rejecting the defendant’s other arguments, and it adopted those reasons as its own.

Concurring in the judgment, Judge Kozinski, joined by Judge Ikuta, wrote that under the majority’s holding, the IMCA is a criminal statute whose application, in violation of equal protection, turns on whether a defendant is of a particular race. Judge Kozinski wrote that he would instead affirm the conviction either by applying the IMCA to all members of federally recognized tribes irrespective of their race, or by holding, consistent with Maggi, that the jury had sufficient evidence to infer that the defendant’s ancestry was from a federally recognized tribe.

Concurring in the judgment, Judge Ikuta, joined by Judge Kozinski, wrote that the court should not continue to define an Indian by the “degree of Indian blood” because this definition disrespects tribal sovereignty and perpetuates the “sorry history” of this method of establishing race-based distinctions.

En banc materials here, here, and here. Panel materials and other materials here, here, and here.