Willi,
The questions have been asked here before. This link will provide you with as much detail on Krefft as is known. He was the technical officer of JG 1 so he frequently accompanied Richthofen on business and would appear in photos with him. He died sometime in the 1920's in Bad Kreuznach. Specific details on his post-war life are unknown.
Lt. Krefft
FliegerJG1