Actually this does seem a violation of Article 13 of the Geneva Convention.

ARTICLE 13

Prisoners of war must at all times be humanely treated. Any unlawful act or omission by the Detaining Power causing death or seriously endangering the health of a prisoner of war in its custody is prohibited, and will be regarded as a serious breach of the present Convention. In particular, no prisoner of war may be subjected to physical mutilation or to medical or scientific experiments of any kind which are not justified by the medical, dental or hospital treatment of the prisoner concerned and carried out in his interest.

Likewise, prisoners of war must at all times be protected, particularly against acts of violence or intimidation and against insults and public curiosity.


Of course under this article -

ARTICLE 129

The High Contracting Parties undertake to enact any legislation necessary to provide effective penal sanctions for persons committing, or ordering to be committed, any of the grave breaches of the present Convention defined in the following Article.

Each High Contracting Party shall be under the obligation to search for persons alleged to have committed. or to have ordered to be committed, such grave breaches, and shall bring such persons, regardless of their nationality, before its own courts.

- it says the people who perpetrated the war crimes should be brought to trail by the US. Which in this case is a court marshal.