Henry Wirtz was hung for his management of Andersonville. Outside of the fact that Wirtz should have been hung for arrogance, his hanging as a war criminal was probably a miscarraige of justice.
The stories I read about Libby Prison suggested more than one war criminal in that venue. That was a Confederate Prison.
I once read that Camp Douglas in Illinois could have served as a nice example of war criminality if the Good Guys had lost that war.
Civil War POW camps struck me as some pretty dreadful places. It seems like they were glossed over by the great authors such as Shelby Foote and Bruce Catton.
The Confederates couldn't even feed their own front-line troops, so Andersonville doesn't surprise me; The Federal POW camps don't have that excuse.