A foreign national detained on suspicion of crime, like anyone else in our country, enjoys under our system the protections of the Due Process Clause. Among other things, he is entitled to an attorney, and is protected against compelled self-incrimination. See Wong Wing v. United States, 163 U. S. 228163 U. S. 228, 238 (1896) ("[A]ll persons within the territory of the United States are entitled to the protection guaranteed by" the Fifth and Sixth Amendments).
Also, while the 5th Amendment states that it applies to "all persons", this is not a part of the constitution in which the definition of a "person" have been extended to apply to corporations and other entities. Compare Citizens United v. FEC, 558 U.S. 310558 U.S. 310 (2010) (holding that the free speech clause of the First Amendment prohibits the government from restricting independent expenditures for political campaigns by corporations, including nonprofit corporations, labor unions, and other associations).
Curcio v. United States, 354 U.S. 118354 U.S. 118, 122 (1957).
The decision to use the 14th Amendment due process clause rather than the 14th Amendment privileges and immunities clause, was made, in part, because the Slaughter House cases, decided by the U.S. Supreme Court in 1874 before the incorporation doctrine had been developed, has narrowly interpreted the privileges and immunities clause as something that applied to only a handful of "rights of federal citizenship.'
But the Slaughter House cases nonetheless are still good law. This is because this precedent was too settled to be easily undone, and because other means had been developed to serve the purposes it was intended to serve when adopted, by the time that sentiment on the U.S. Supreme Court had changed to accept the demise of slavery, when the U.S. Supreme Court ended the "separate but equal" doctrine of Plessy v. Ferguson, 163 U.S. 537 (1896), in Brown v. Board of Education, 347 U.S. 483 (1954).
Justice Thomas argued in his dissent in Saenz v. Roe that the Bill of Rights should instead have been incorporated via the privileges and immunities clause of the 14th Amendment, and that the Slaughter House cases and the various cases establishing the incorporation doctrine as arising under the due process clause of the 14th Amendment should be overruled.
But, unlike the 5th Amendment right, this right arising under U.S. treaties has only rarely been afforded an exclusionary rule type protection to foreign criminal defendants if it is denied, in the way that 5th and 6th Amendment violations of the rights are foreign criminal defendants are protected.