I don't have a William Pinkney Mitchell listed in my "Encyclopedia of Quantrill's Guerrillas." I also checked Donald Hale's books (all 3 volumes) of "Branded as Rebels" and he was not listed there. Now, saying that, sometimes Quantrill's men fought in many battles with different Confederate groups. So, there is a possibility that perhaps your ancestor may have fought in a battle that some of Quantrill's men fought in.

Rose Mary Lankford
hickoryflatoutlaws@centurytel.net