Wow, so never mind all that "reasonable doubt" stuff. If we claim that they were "most likely stolen" then that is good enough.
If he was investigated for "illegal possession" during the 30's or 40's it may not have been for those exact coins. The Federal government claimed that gold coins were illegal for Americans to posses at all back then. Gold was presumably made illegal to own back in 1933 (One of many crimes that FDR perpetrated against our Republic) It was not repealed until the 70's.