BONNE TERRE, Mo.—A Missouri man was put to death Tuesday for killing three workers while robbing a convenience store nearly three decades ago, an execution performed over objections from racial justice activists, lawmakers, and even the pope. Ernest Johnson died from an injection of pentobarbital at the state prison in Bonne Terre. He silently mouthed words to relatives as the process began. His breathing became labored, he puffed out his cheeks, then swallowed hard. Within seconds, all movement stopped. In his written last statement, Johnson said he was sorry “and have remorse for what I do.” He said he loved his family and friends and thanked those who prayed for him. Johnson was pronounced dead at 6:11 p.m., nine minutes after the dose was administered. A corrections department spokeswoman said four relatives representing all three victims were present. Johnson’s witnesses included relatives and his lawyer. No relatives spoke after the …