"Can anyone source the claim that Nathan Bedford Forrest removed the skin of African-Americans with his sword?"
I don't believe that anyone can source the claim period. The last time I heard about his sword was when the author "Shelby Foote" noted in Ken Burns Civil War series that a descendant of General Forrest had allowed him to pick up the sword. As far as I know the sword in question still is in the hands of the Forrests' descendants. When Forrest died in 1877 dozens of blacks attended his funeral. They did so out of respect for the General. He was the first grand wizzard of the newly formed KKK, however that organization was formed to help protect the Southern people against the carpetbaggers after the War. The KKK in 1867 and the KKK years later had a totally different agenda. Forrest left the KKK when it was not being used as it was orginially intended. It is true that Nathan Forrest was also a slave dealer prior to the War in Memphis, TN. When his partner started spliting up the black families he was furious and let his partner know of his feelings. In a strange sort of way you might be able to say that Forrest was the civil rights leader of his day insofar as the selling of slaves. People have a hard time understanding this in my opinion because things were so different in pre Civil War days and many people try to put the men in todays time.

General Forrest was the leader at Fort Pillow and as such the responsibility for the action of his troops fell to him. When Forrest demanded the surrender of the Fort, it is my understanding that the Union forces may have been buying some time to improve their military position. When the attack began it was hot and furious and I do believe that some blacks were probably killed while trying to surrender. However I also believe that General Forrest would never have issued such an order and did everything he could do to stop it once he found out what was happening. I also believe that the North would have had no problem in trying General Forrest for those so called crimes if they thought they could have. There was a commison to look into the inquiry of Fort Pillow but no charges were filed against Forrest.

The 6th and 7th United States Tennessee Cavarly Regiments were raised essentially from West Tennessee. There was no love lost between Forrest and these units. Generals like George S. Patton even took many of Forrests' ideas and places like West Point even taught some of his tactics. Fairly impressive since he did not even have a high school education. Forrest remains one of the greatest military tactians of American History. He is also in my opinion one of the most misunderstood men in American History. It is amazing to me how many well educated people do not know who General Forrest really was. Directly after the War Forrest raised money in Memphis for the blacks as an example. Perhaps that was one of many reasons why so many blacks turned out for his funeral.

Forrest was asked to speak at the 1868 Democratic Convention held in New York City in 1868. It was here that a slanderous statement was made by General Judson Kilpatrick saying something along the lines that Forrest had tied blacks up to fences and then set them on fire. When Forrest read Kilpatrick's speech he immediately ask for a duel wanting to use sabers on horseback. Of course Kilpatrick declined the invitation. Of course Kilpatrick probably used this statement for political purposes just as Mr. Barton and Mr. Beck used their statements about Forrest for political purposes and television ratings.