In an extraordinary admission that threatens to further damage its standing, the Irish Republican Army said Tuesday that it was willing to shoot the killers of Robert McCartney, a Northern Ireland Catholic slain by a gang that included I.R.A. members. The killing of Mr. McCartney, a 33-year-old forklift truck driver stabbed to death after a bar brawl on Jan. 30, has convulsed Northern Ireland politics, creating a crisis for the I.R.A. and its political wing, Sinn Fein, just months after accusations that the I.R.A. was behind a $50 million bank robbery.Full Story