As it happens, I'm working on a book of stories from Andersonville that are not usually told, and so I've been pouring over the Atwater List, the NPS Database and the original Confederate List of prisoner departures, looking for "citizen" (not civilian) prisoners. There are a few hundred of them.
The man you're looking for has different names on each of the sources, but they all list the same grave number, so they all mean the same person. He's listed as "Citizen, Indiana" and his name is variously given as B. Tiser, B. Tucer, and B. Tweer, all of which are probably misreading of the same name. It's kind of unusual for a state to be listed for a citizen, but that's what was written.
Citizen prisoners were frequently employed by the Quartermaster's Office, usually as Teamsters, hauling equipment for the military, but I've also found wagoneers, sutlers, watermen, a railroad employee, a topographical engineer, and a couple of employees from the American Telegraph Company. Being a citizen teamster paid pretty well - more than the soldiers made, according to one ad - but if you were captured and died, there was no provision for a pension for your family, so your wife and kids were screwed.
There are just over 100 citizen graves in the cemetery.
Hope this helps.
The highest ranking officer held at Andersonville was Col. W H Noble, of the 17 Connecticut. I've heard that officers who commanded blacks were sometimes put in Andersonville. I think that was the case with Major Bogle (sp?). There was also a place toward the railroad tracks where officers were held for a while.