ST. PAUL, Minn. - While searching for her birth parents two years ago, Mariah Mills found more than she bargained for: A hero of Sept. 11, 2001. Mills’ biological father, who had given Mills up for adoption when he and his then-girlfriend were in college, was Tom Burnett, a leader of a group that fought back on United Flight 93 before it crashed in Pennsylvania on Sept. 11, 2001. Mills, 21, learned about her birth father in 2004 - after she turned 19, the legal age in Minnesota for requesting a birth certificate with names of birth parents - and...