Roger Clemens’ trial on perjury charges begins Wednesday with jury selection—and his best friend and former teammate, Andy Pettite, could be one of the prosecution’s best witnesses. Pettite previously claimed in a sworn affidavit that Clemens had admitted to him to using human-growth hormone in 1999 or 2000. (The affidavit was part of the congressional hearing during which Clemens is accused of perjuring himself.) The courtroom will bring Clemens and Pettite face to face. “Andy is going to be uncomfortable. I’m going to be uncomfortable. We’re all going to be uncomfortable,” former Yankees catcher John Flaherty tells The New York Times. Clemens’ former trainer, Brian McNamee, will also be a key witness.