Former KB Home chief Bruce Karatz turned to a powerful ally Thursday in his defense against stock-options backdating charges, presenting former Los Angeles Mayor Richard Riordan as the first of his character witnesses. Riordan, who served as mayor from 1993 to 2001, told jurors at the federal courthouse in Los Angeles that he's known Karatz 30 years, considers him a close friend and does not believe he would knowingly commit a crime.