In the case of Compagna et al. v. Hiatt, Warden (1950), the petitioners were three Italian nationals who had been convicted in a U.S military commission for war crimes committed during World War II while they were serving as German soldiers. They challenged their convictions on several grounds including that the United States lacked jurisdiction to try them and that they did not receive fair trials because of alleged procedural errors by the military commission. The Supreme Court rejected these arguments and upheld their convictions. The court ruled that under international law, individuals can be held accountable for war crimes regardless of nationality or where those crimes occurred. It also found no merit in claims about unfair trial procedures, noting that all defendants had access to counsel and opportunity to present evidence in their defense. This decision affirmed broad authority for U.S military commissions to prosecute war criminals captured during armed conflicts irrespective of national boundaries or citizenship status.

In the dissenting opinion for Compagna et al. v. Hiatt, Warden (1950), Justice Frankfurter argued that the majority's decision was a departure from established legal principles and precedent regarding habeas corpus petitions. He contended that the petitioners' claims were not new or novel but rather had been previously adjudicated by military tribunals, which should have been given deference by civilian courts under existing law and practice. Furthermore, he disagreed with the majority's interpretation of international law as it applied to this case, asserting that they misapplied its provisions in order to reach their conclusion. Finally, he expressed concern about potential implications of this ruling on future cases involving war crimes committed during World War II.