NEW YORK — A gunman who announced online that he was planning to shoot two "pigs" in retaliation for the police chokehold death of Eric Garner ambushed two officers in a patrol car and shot them to death in broad daylight Saturday before running to a subway station and killing himself, authorities said.The suspect, 28-year-old Ismaaiyl Brinsley, wrote on an Instagram account: "I'm putting wings on pigs today.