COLUMBIA, S.C.— A firing squad on Friday executed a South Carolina man who killed an off-duty police officer, the second time the rare execution method has been used by the state in the past five weeks. Mikal Mahdi gave no final statement and did not look to his right toward the nine witnesses in the room behind bulletproof glass and bars once the curtain opened. He cried out as the shots hit him, and his arms flexed. A white target with the red bull’s-eye over Mahdi’s heart was pushed into the wound in his chest. He groaned two more times...