EL PASO - She lived a double life. At the border crossing, she was Agent Garnica, a veteran law enforcement officer. In the shadows, she was "La Estrella," the star, a brassy looker who helped drug cartels make a mockery of the U.S. border. Martha Garnica devised secret codes, passed stacks of cash through car windows and sketched out a map for smugglers to safely haul drugs and undocumented workers across the border. For that she was richly rewarded; she lived in a spacious house with a built-in pool, owned two Hummers and vacationed in Europe. For years, until an...