Malcom "Mal" Reynolds wrote:

I stand by that: by definition any American Citizen who served in an
enemy military and held in an American POW camp would be guilty of
Treason. Since there were no indictments or trials for Treason during
the war, it stands to reason that no American citizens were captured
and/or held in these POW camps

Treason is a criminal offense. These foreign soldiers were not criminals.
You'll note that not any were tried for murder or attempted murder for
shooting at our troops on the battlefield.

The laws of war are different from the criminal laws; the two systems have
different offenses, different rules of evidence and procedure, different
standards of proof, and different appellate procedures. Under the usual and
customary laws of war, the accused is not entitled to a lawyer, an
indictment by a grand jury, a jury trial, compulsory process for obtaining
witnesses, or the right to remain silent. All these we guarantee to CRIMINAL
defendants, but not necessarily to others (unlawful enemy combatants,
juveniles, the mentally ill, contagious disease carriers, civil contemptors,
and others).

In other words, not everybody who does a nasty thing is subject to criminal
law.