Just before 28-year-old Ismaaiyl Brinsley approached a squad car and fatally shot two officers in Brooklyn, he turned to people on the street, asked them to follow him on Instagram and said, "Watch what I'm going to do," police said Sunday. The Brooklyn-born killer had a long criminal record which included at least 19 arrests in Georgia and Ohio as well as spending two years in prison for gun possession, Chief of Detectives Robert Boyce said. The gunman also had a history of mental instability, which included an attempt to hang himself a year ago. Brinsley's mother said she believed he may have been on medication at some point, but it remains unclear if he had mental illness. Authorities said Brinsley also spoke out against police and government online, expressing "self-despair and anger at himself and where his life was," Boyce added. He also traveled frequently between the South and New York, where he had a child in Brooklyn. Investigators are still trying to determine whether the Brinsley participated in any protests over the deaths of Michael Brown and Eric Garner, whose names he mentioned in his online threat just before the shooting. Brinsley went on a shooting rampage Saturday, wounding his ex-girlfriend in Baltimore before killing Officers Rafael Ramos and Wenjian Liu in Brooklyn's Bedford Stuyvesant neighborhood. He shortly after fled to a subway and committing suicide.