Steve,

This guy is new to me, but I think I found him listed in Joanne Chiles Eakins' landmark 1995 "Missouri Prisoners of War." This quotes the files from the National Archives to say that CPT William Mosby of Company C or 1st MO Regiment was captured Batesville, AR on 4 Feb 1863. He was sent to Gratiot Street Prison (formerly McDowell Medical College) in St. Louis but transferred 24 Feb 1863 on to Camp Chase in Ohio. Beware of these details, as those Union clerks made lots of mistakes on these things. I found nothing about his subsequent adventures.