In Leonard v. United States (1963), the petitioner, a member of the U.S. Navy, was convicted by a court-martial for premeditated murder and sentenced to death. The Supreme Court had to decide whether it could review this conviction despite not having direct appellate jurisdiction over court-martial decisions according to Article III of the Constitution and 10 U.S.C § 871(c)(1). The Court held that it did not have authority to review convictions made by courts-martial as they are outside its constitutional mandate. It further clarified that military tribunals are part of the war powers given by Congress and President under Article I Section 8 Clause 14, rather than judicial power under Article III of Constitution; hence their decisions do not fall within Supreme Court's purview unless explicitly provided for in law.

In the dissenting opinion for Leonard v. United States, Justice Douglas argued that the petitioner's conviction should be overturned due to a violation of his Fifth Amendment rights against self-incrimination. He contended that when Leonard was asked by customs officials if he had anything to declare and responded negatively, this constituted a form of compelled testimony because he was legally obligated to respond. When it was later discovered that Leonard did have undeclared items in his possession, this response became incriminating evidence used against him at trial. Justice Douglas believed this violated the principle that no person "shall be compelled in any criminal case to be a witness against himself," as stated in the Fifth Amendment. Furthermore, he expressed concern about potential abuses of power by government officials who could manipulate situations so individuals unwittingly incriminate themselves during routine questioning or administrative procedures.