Simply put, you don't know what you are talking about.
We had just fought a war for our survival and bills of attainder had been used. Attainder laws were thus well known and discussed at length at the Constitutional Convention and the Virginia Ratifying Convention. Our Framers feared such power in the hands of evil men and denied it to our federal and state governments.
For Hussein to decide what constitutes a capital offense (make law), decide who shall be killed (serve as judge and jury), and then execute his one man law, is a gross violation of separation of powers denied him by our Constitution in the attainder prohibition.
Of course they did so, but that still does not apply to the age old laws of war with respect to civilians engaging in combat and combat intelligence activities without a commission from a sovereign to do so. The British tended to treat captured Americans during the Revolutionary War as rebels, insurrectionists, and traitors to a great degree; but the surrenders of so many British troops and American Tories induced the British authorities to moderate these policies to some extent andd treat the American captives moer as cpatureed prisoners of war and enemy detainees under the Laws of War. This british change of policy in certain occcasions was based upon the theory that the captives weree in the commissioned service of the rebellious legislatures exercising their limited sovereignty as colonial legislatures.
A roman commander waged war upon a Celtic tribe in Northern Italy, with whom the Republic of Rome had an ongoing truce or peace treaty, i don’t remeber which. The Celts seent an emissary to the Roman Senate to sue for the breach of the peace, and they demanded the surrender of the Roman commander for his violations of Roman law by engaging in war without consent of the Roman Senate. The Roman justice found the Roman commander guilty and surrendered him to the Ceelts for punishment.
In another case, a young julius Ceasar was captured and held for ransom by Illyrian pirates. He eventually negotiated for his releease by the payment of the ransom. The terms of the agreement with the pirates requireed Ceasar to agree to not retaliate against the pirates for his ransom. After the pirates released Ceasar, he returned with the Roman army and slauhtered them and devastated their pirate communities. The surviving pirates sued Ceasar in Rome with the legal complaint that Ceasar unalwfully abrogated his treaty with the Pirates, promising no armed retaliations after being released. Ceasar defeended his actions by noting pirates had no legal rights among any civilized nations, and no contract made with a an outlaw pirate was enforceable in law. The Roman Seenate found in favor of Ceasar while noting pirates and brigands were subject to death at the hand of any military or civilian person in any land.
That is why the Bill of Attainer is not applicable to this situation. The Constitution explicitly adopted the Law of nations with respect to thsoe persons engagedd in piracy on the high seas and violations of the Law of Nations respecting waging war and brigandage.
Are we to understand you are implicitly arguing President Franklin Delano Rooseevelt was also a criminal for ordering the U.S. armed forces to bomb a building and French military target in Casablance in 1942 which killed one or more U.S. citizens within the neutral French building?