Hi Derek,
Have you looked up on Gengophers.com, either Sasser, or Wilhelm/William Sasser? There are a number of books listed for the Sasser name from Germany, GA, NC, MI, Maryland, Idaho, Texas. Perhaps you may find some info in one or a few of these online books. A few of the books from Germany are written in German, so unless you know the language, you might have to have them interpreted.
I have a friend who is a Sasser by marriage and I believe her ex-husband's family (Sasser) was from Michigan.
Hope this helps you find a place to start.