As far as POWs are concerned there should have been a lot more people on both sides charged with those crimes. Major Wirz was a scapegoat.
Easy to scapegoat - foreign born, incompetent & a nasty personality.
Indeed he was-— as Col.Wirz was...Swiss. Something never discussed (as the victors write the history) was the needless deprivations of Point Lookout or Johnson’s Island- the Union had the money and supplies to treat prisoner’s decently— but the people who were in that command (and indeed the very corrupt Sec. Stanton himself lining his pockets- an evil man), were corrupt grafters leaving prisoners to horrible condition and doing a brisk trade in humans, misery, food and supplies. These were never (rarely) exposed by Provost Marshal system.
By far the worst, never discussed at all was Camp Douglas— in Chicago— the largest and most corrupt hell-hole in the Union POW system. Chicago— producing the prison town we know today filled with corrupt democrat pols and their mob pals.
The fact is— that Anaconda (the Union navy Blockade of the South) worked quite well,and early on produced deprivations for the CSA that required re-distribution of what they had, and POWs got essentially the same privations that the average CSA soldiers did (no shoes, no food, no clothes). There are documented cases of CSA prison personnel being fully disciplined as there are of Union personnel done the same for POW abuse. The South was starving, and Sherman didn’t help.
Camp Sumter was created in February 1864....late in the war and out of a preponderance of Union POWs captured in the winning Union campaigns. Sherman’s March to the Sea began in November 1864 until Dec. 21. notably bypassing Andersonville (overfilled beyond capacity and the horrors there as much caused by Sherman’s actions as Anaconda and the waging of Civilian war crimes by his “bummers”. The first use of total war).