This may help with further research on Rene Jentgen.
The Ohio Death Index lists a Rene Jentgen born 5 Aug 1931 who died 3 Nov 2000 in Canton, OH,Stark Co..which is close to Akron. The record stated that he had been residing in Carroll Co OH.It also stated he served in the Army. You might try to obtain military record. No mention was made of San Bernardino CA on that record.