I might suggest that you fill out a "tracing form" with the American Red Cross. They have a wonderful relationship with the German Red Cross and they may be able to help. My great-uncle was lost during World War II and the family didn't know what happened. I filled out a tracing form and 3 months later got an envelope with 11 pages of documents that included where and how he died and where he was buried. It was amazing. The service is free. Here's a link: http://www.redcross.org/portal/site/en/menuitem.53fabf6cc033...
Good Luck!