Some time ago my roommate and I ended up discussing atrocities that both sides committed during the war. Immediately acts against captured USCT soldiers by Confederates was mentioned, however other acts, that did not involve black soldiers, were brought up. One story was from my roommate who read an account about a green Federal regiment marching in Tennessee one night during the War. Some local partisans ambushed the Federals, scattering most of the regiment with around 20 members of the regiment becoming captured. The captives were led to a ravine where they were summarily executed with a single shot to the back of the head. Unfortunately I don't know any more about the story or what regiment it happened to.
That story reminded me of one described by a German soldier in East Tennessee in winter of 63-64. In letter to dated February 23, 1864 by Gottfried Rentschler of the 6th Kentucky (US) Infantry.
Two Germans in the Civil War: The Diary of John Daeuble and the Letters of Gottfried Rentschler. Edited and Translated by Joseph R. Reinhart. Page 48On the 6th we came through Georgetown, a small town that had little damage; and camped overnight on the farm of Major Baird of the 3rd Tennessee Cav. Regt. There, many of the country people in the neighborhood sought us out and gave an account of how dreadfully they had suffered from the Rebels. When Wheeler made the last invasion in the area, one of his soldiers, by the name of Roberts, went into the house of a certain Carter (the Carters consist of a very large family in East Tennessee and are all very good Union people) and shot Robert Carter, a young man, poked his eyes out, shoved them into this pocket, and went to his mother, to whom he said that he had killed Bob Carter. She said, "You did not do that." He pulled the eyes out of his pocket and threw them on the table saying: "Here, if you do not believe me here are the eyes of the son of a bitch." This is only one of the numerous atrocities. Here and there the Southern barbarians have most certainly received their rewards for their cruelty as, e.g., the Sesech who hideously beat an old man whose son was a lieutenant in a Tennessee regiment. When the lieutenant when to Knoxville with his regiment and came through his home area, and learned who committed this atrocity on his old father, he went into the house of the Sesech, pulled him into the street, and shot a bullet through his head.
Also I remembered this account by Sergeant Patrick Henry Goodrich of the 20th Connecticut Infantry. In a letter dated Sept. 22, 1863 near Raccoon Ford, Goodrich describes the battle of Chancellorsville.
Civil War Letters of Sgt. Patrick Henry Goodrich: A Soldier in the Connecticut Twentieth Regiment, Company D. Edited by Lawrence P. Cogswell, Jr. page 43I was in the trenches until 6:00 when the firing commenced for the day. It was kept up for 1/2 an hour or so up on the right of us when the Rebs were driven back down towards us. There was one of our batteries and two regts. in front of us. One of them were ____. The Rebs fired on them. They fired one or two rounds, and then were ordered to charge. Instead of doing that, they ran back, the cowardly sneaks. They may talk as much as they please about ____. If they are all like that regt., they may as well be sent home or be put in the 11th Corps. After they had left, the Rebs took the battery and turned it on us. Their infantry then came up with a yell and shouting through the hollow in front of our Regt. We let them get pretty up, then we raised up and let them have it. THis was too much for them, and they turned and they turned on a double quick. Lots of them fell before they got out of the hollow. Some of them lay down in the bushes, and as soon as the firing was over, got up and waved their hats and wanted to come into our lines. Several did come but were shot by our men who said they had seen too much of their barbarity. THey would now shoot any hat they saw raised out of the bushes. After driving them back, we lay down in our trenches.