Why did miller decide to let the german soldier go free?

Captain John H. Miller was an assertive but esteemed leader in the army. Though he showed toughness on the outside, Captain Miller also tends to hide his vulnerable side when he privately cried loosing a medic due to a rare error. This then, tends to explain why he released the held captive German soldier. 

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.