Here are some relevant parts of the Lieber Code:
Art. 36.
If such works of art, libraries, collections, or instruments belonging to a hostile nation or government, can be removed without injury, the ruler of the conquering state or nation may order them to be seized and removed for the benefit of the said nation. The ultimate ownership is to be settled by the ensuing treaty of peace.
In no case shall they be sold or given away, if captured by the armies of the United States, nor shall they ever be privately appropriated, or wantonly destroyed or injured.
Art. 37.
The United States acknowledge and protect, in hostile countries occupied by them, religion and morality; strictly private property; the persons of the inhabitants, especially those of women: and the sacredness of domestic relations. Offenses to the contrary shall be rigorously punished.
This rule does not interfere with the right of the victorious invader to tax the people or their property, to levy forced loans, to billet soldiers, or to appropriate property, especially houses, lands, boats or ships, and churches, for temporary and military uses
Art. 38.
Private property, unless forfeited by crimes or by offenses of the owner, can be seized only by way of military necessity, for the support or other benefit of the army or of the United States.
Art. 42.
Slavery, complicating and confounding the ideas of property, (that is of a thing,) and of personality, (that is of humanity,) exists according to municipal or local law only. The law of nature and nations has never acknowledged it. The digest of the Roman law enacts the early dictum of the pagan jurist, that "so far as the law of nature is concerned, all men are equal." Fugitives escaping from a country in which they were slaves, villains, or serfs, into another country, have, for centuries past, been held free and acknowledged free by judicial decisions of European countries, even though the municipal law of the country in which the slave had taken refuge acknowledged slavery within its own dominions.
Art. 43.
Therefore, in a war between the United States and a belligerent which admits of slavery, if a person held in bondage by that belligerent be captured by or come as a fugitive under the protection of the military forces of the United States, such person is immediately entitled to the rights and privileges of a freeman To return such person into slavery would amount to enslaving a free person, and neither the United States nor any officer under their authority can enslave any human being. Moreover, a person so made free by the law of war is under the shield of the law of nations, and the former owner or State can have, by the law of postliminy, no belligerent lien or claim of service.
Art. 44.
All wanton violence committed against persons in the invaded country, all destruction of property not commanded by the authorized officer, all robbery, all pillage or sacking, even after taking a place by main force, all rape, wounding, maiming, or killing of such inhabitants, are prohibited under the penalty of death, or such other severe punishment as may seem adequate for the gravity of the offense.
A soldier, officer or private, in the act of committing such violence, and disobeying a superior ordering him to abstain from it, may be lawfully killed on the spot by such superior.
Art. 45.
All captures and booty belong, according to the modern law of war, primarily to the government of the captor.
Prize money, whether on sea or land, can now only be claimed under local law.
Art. 46.
Neither officers nor soldiers are allowed to make use of their position or power in the hostile country for private gain, not even for commercial transactions otherwise legitimate. Offenses to the contrary committed by commissioned officers will be punished with cashiering or such other punishment as the nature of the offense may require; if by soldiers, they shall be punished according to the nature of the offense.
If the owner has not fled, the commanding officer will cause receipts to be given, which may serve the spoliated owner to obtain indemnity.