reading the conan wiki page, i'm starting to think it's Sonoko's father, Shiro Suzuki. i mean, we know he has lots of money, owns a giant corporation, and Sonoko was introduced early enough so that if her father turned out to be responsible for the BO it would at least be connected. aoyama mentioned in an interview that the name of the boss has been given, but not the appearance, which fits since Suzuki has been mentioned but not seen.