Commissioner Bud Selig has named former Sen. George Mitchell to head a full-scale investigation into the past use of performance-enhancing drugs in Major League Baseball. The announcement came at a press conference at the Commissioner's office on Thursday. The probe was spurred by recent allegations made in a book that targets San Francisco Giants slugger Barry Bonds and Gary Sheffield and Jason Giambi of the New York Yankees, among a number of other former Major Leaguers.