Gentlemen,
If he was held there as a POW, he should have a "slip" in his Compiled Military Service Records reflecting so. A slip would have been produced by the clerks at the War Department (post-war) when a soldier's name is reflected in an original document or record and that would have been placed in a file with his name. I recommend that you get a copy of his CMSR.
Respectfully,
Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Volunteer Infantry Regiment
http://39thgavolinfrgt.homestead.com/39thHomepage.html