I found one David Thomas from Mississippi listed in the Archives. He is listed as: David H. Thomas, Tec5, US Army, DNB, Serial Number 44048777. DNB is Died, Non-Battle, and means he died from a cause other than combat, such as disease, accident, etc. If this is your grandfather, you can use this info to try and get his service record. Directions on how to do so can be found at this site: http://www.archives.gov/facilities/mo/st_louis/military_personnel_records/standard_form_180.htmlhttp://www.archives.gov/facilities/mo/st_louis/military_personnel_records/standard_form_180.html They had a big fire in 1977 and the odds are against you, but it's worth a try.
You can also send for his Individual Deceased Personnel File (IDPF). As others in the forum have addressed, the info found in an IDPF can be graphic. If you pursue this resource, be prepared for that possibility. Send your request to: US Total Army Personnel Command ATTN: TAPC-PAO (FOIA) 200 Stovall Street Alexandria, VA 22332-0404 Be sure to cite the Freedom of Information Act in your request. (Incidentally, I looked for this David Thomas in the Archives list of WWII POW's, but did not find him.)