The shooter, Ismaaiyl Brinsley, was said to have a lengthy criminal record. He was arrested 15 times in Georgia for assorted crimes, four times in Ohio and New York Police Department's Chief of Detectives Robert Boyce told reporters on Sunday.
Ismaaiyl Brinsley, 28, has roots in Brooklyn and his mother who he is estranged from lives in New York borough.
Authorities said Brinsley walked to the patrol vehicle where the officers were sited and shot the to death with four shots on Saturday.
Jaden Ramos, 13, wrote "Today is the worst day of my life" on facebook today about his slain father, Rafael Ramos.
"Today I had to say bye to my father who was there for me everyday of my life, he was the best father I could ask for. It's horrible that someone gets shot dead just for being a police officer. Everyone say they hate cops but they are the people they call for help. I will always love you and I will never forget you. RIP Dad."
Ramos and Wenjian Liu were assigned to an area of the borough that has more crime than their usual beat in downtown Brooklyn, police said.
Witnesses saw Brinsley walked to the car and assume what they described as a shooting stance. New York Police Commissioner, William Bratton, said Brinsley fired several times. Ramos and Liu were shot in the head. The officers were shot with no warning, no provocation, "they were quite assassinated."
Brinsley was found dead of a self-inflicted gunshot wound at a nearby subway station, authorities said.
Dozens of officers gathered as the families of the fallen officers rushed to Woodhull Medical Center on Saturday.
Ramos just turned 40; Liu had just been married for two months. Both had a dream of becoming police officers, said Bratton.