Killer of Police Officers Had Long Criminal History

The gunman who fatally ambushed two police officers in their squad car had a long criminal record, a hatred for police and the government, and an apparent history of mental instability that included an attempt to hang himself a year ago, authorities said on Sunday.Moments before opening fire, Ismaaiyl Brinsley approached people on the street in Brooklyn and asked them to follow him on Instagram, then told them, “Watch what I’m going to do,” Chief of Detectives Robert Boyce said.A portrait of the Brooklyn-born gunman emerged as big-city police departments and union leaders around the U.S. warned officers to change their routines and insist on extra backup a day after the attack.