Berkshire Hathaway Inc. (NYSE:BRK.A) (NYSE:BRK.B) repurchased $1.2 billion of stock yesterday. There was a question as to who the mysterious seller of $1.2 billion of shares was. Whitney Tilson who bought more Berkshire shares yesterday, has a theory as to who it is. He also discusses the buyback in general below in an email we received. This email is focused on Berkshire’s buyback. 1) A fun tidbit: on 12/12/12 Warren Buffett bought $1.2 billion at 120% of book and we peg Berkshire Hathaway Inc. (NYSE:BRK.A) (NYSE:BRK.B)’s intrinsic value at $120 per B share. 2) David Reilly of the WSJ usually writes good…