Clue from a kidnapped victim
Detective Shinichi investigated the scene of the crime. Apparently, the fifth richest man in Crimeville, Bill Richman, had been kidnapped! The only thing at the scene was a note left, no doubt, by Bill Richman while he was being kidnapped. It read, "First of January, Fourth of October, Fifth of March, and Third of June." Detective Shinichi knew this note was accusing the kidnapper. He had to decide which one it was, out of:
Jack Richman, Bill Richman's son and heir,
John Jacobson, Richman's employee, or
June Richman, Bill's wife.
Detective Shinichi discovered what the note meant, and promptly told the authorities who it was.
Hint
No, the note has nothing to do with any calendar dates.