"Targeted executions violate well-established principles of international law.
[....] Extrajudicial executions are unlawful, even in armed conflict, In a 1998 report the United Nations Special rapporteur on extrajudicial, summary or arbitrary executions noted that 'extrajudicial executions can never be justified under any circumstances, not even in time of war.' The U.N. General Assembly and Human Rights Commission, as well as Amnesty International, have all condemned extrajudicial executions.
[The WW II victory in 1945] After the Holocaust, Winston Churchill wanted to execute the Nazi leaders without trials. But the U.S. goveernment oppose the extrajudicial execution of the Nazi officials who commited genocide against millions of people." [The result was the Nuremberg War Crimes Tribunal.]
Prof. Marjorie Cohn article "American Justice."