(Keizer, OR)  --  An autopsy will be conducted on the body of a Keizer man who had gone missing.  Authorities say 54-year-old Robert Allen Knupp was found dead in a field in rural Marion County yesterday.  Knupp was reported missing June 8th after his car was found at a rest area off I-5 south of Salem.  There's been no word on how long it had been since Knupp died.