It appears that his birthplace "Roitsch" is located in Saxony-Anhalt with the spelling Roitzsch - however, there appear to be two such places. Infanterie-Regiment 16 is associated with Oldenburg so it only stands to reason that he would have resided there. The regiment is perpetuated by Panzerbataillon 314:http://www.pzbtl314.de/oldenburgische.htm
After the war, the veterans of IR16 formed a regimental association (Kameradschaft "Oldenburgische Infanterie") along with veterans of the First World War from IR91. I have an interest in the regiment from the first war and so it turns that some time ago I managed to some of the association's newsletters. I will check them over the next few days to see if there is anything about him in any of them.
I'm wondering if the documents that you have would be his Soldbuch:http://www.soldbuchweb.com/sbpg02.htm
The surname is extremely uncommon in Germany; there are only four telephone book listings with the name (five if you include Kriß):http://www.verwandt.de/karten/absolut/kriss.htmlhttp://www.verwandt.de/karten/absolut/kri%25C3%259F.html
Not sure about contacting people out of the blue about something like this, esp. when it deals with WW2.