Killing one's own combatants who have surrendered would generally be considered illegal under domestic laws and could be classified under various legal frameworks depending on the jurisdiction:

Military Law: Most countries' military codes explicitly prohibit executing or harming soldiers who have surrendered or are no longer able to fight. This is to maintain discipline, morale, and to uphold the principle of protection for those who have laid down their arms.

National Law: Acts like murder or manslaughter would apply in most legal systems, even if committed during wartime. Military personnel are still subject to national criminal laws when actions exceed the bounds of military operations or discipline.

International Humanitarian Law (IHL): While IHL primarily focuses on the treatment of enemy combatants, the principles of humanity and unnecessary suffering apply universally. Harming or killing one's own personnel who have ceased to be combatants would run counter to these principles, though the legal pathways might be more convoluted or subject to internal military justice systems rather than international tribunals.

Human Rights Law: Depending on the context, such acts could also be examined under human rights frameworks, especially if there's an element of extrajudicial killing, which is prohibited under international human rights law.