Prosecuting the Confederate leaders was indeed difficult, so the yankees found another venue to let out more of their blood lust. And don't bother to ask if the commanders of Camp Douglas, Camp Chase or Elmira were ever charged with any crimes. Like Wirz, they followed orders. The difference is they had provisions and they withheld provisions, which resulted in the murder of tens of thousands of war prisoners.
http://www.spartacus.schoolnet.co.uk/USACWwirz.htm
Wirz was found guilty on 6th November and sentenced to death. He was taken to Washington to be executed in the same yard where those involved in the assassination of Abraham Lincoln had died. Alexander Gardner, the famous photographer, was invited to record the event.
The execution took place on the 10th November. The gallows were surrounded by Union Army soldiers who throughout the procedure chanted "Wirz, remember, Andersonville." Accompanied by a Catholic priest, Wirz refused to make a last minute confession, claiming he was not guilty of committing any crime.
Major Russell read the death warrant and then told Wirz he "deplored this duty."Wirz replied that: "I know what orders are, Major. And I am being hanged for obeying them."
After a black hood was placed over his head, and the noose adjusted, a spring was touched and the trap door opened. However, the drop failed to break his neck and it took him two minutes to die. During this time the soldiers continued to chant: "Wirz, remember, Andersonville."