Why didn't the United States hang（kill） the Japanese emperor after winning World War II?

Following the surrender of Japan, Emperor Hirohito was not prosecuted for war crimes at the Tokyo War Crimes Tribunal even though the Japanese had waged war in his name. The head of the Allied occupation of the country, Douglas MacArthur, believed that a cooperative emperor would facilitate a peaceful occupation and other U.S. postwar objectives. MacArthur therefore excluded any evidence from the tribunal which could have incriminated Hirohito or other members of the royal family.[1] In 1946, Hirohito was pressured by the Allies into renouncing his divinity. Under Japan's new constitution drafted by U.S. officials, his role as emperor was redefined in 1947 as "the symbol of the State and of the unity of the people".