It has been a week since you posted. I don't know if anyone has contacted you via e-mail, or otherwise. In the event that you have not received a response, and until you get more informed aid, here is some info that may be of interest to you.
Sergeant Mitchener is listed in the ABMC database. You can access that info by doing a search at this web page: http://www.abmc.gov/searchww.htmhttp://www.abmc.gov/searchww.htm
These web pages have info pertinent to his bomb group: