Grenade used in shootout with Mexican police linked to alleged U.S. arms trafficker

      |A grenade used in the murder of three Mexican police officers has been linked to an alleged U.S. arms trafficker that U.S. officials left on the streets to operate, long after they had evidence of his crimes. Officials from Mexico and the U.S. are not publicly talking about the case. CBS News investigative correspondent Sharyl Attkisson reports.