A very biased source that goes into this is the recent reprint (2003) of William Monks' 1907 memoir "A History of Southern Missouri and Northern Arkansas" reprinted by The University of Arkansas Press, and edited by the very capable John F. Bradbury and Lou Wehmer (who also read this forum, I think). Monks gives you the Union perspective on this aspect and he was right in there killing men with the rest of them. He served as a northern cavalry commander and served throughout the entire war, so he knows what he writes about, although he gives his slant--of course! This book is still in print, as far as I know.
My books touch on this subject, but they don't go into the detail that an eyewitness or participant account does.