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.
According to authorities, the account also displayed a handgun and a message that said it might be the pster's last message.
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.
Bratton also said, "One of the unfortunate realities of policing is that you put on a blue uniform and you become part of the thin line between us and anarchy."
He sent a memo to the NYPD officers about the killings saying the officers were "targeted for their uniform, and for the responsibility they embraced: to keep the people of the city safe."
"That is no indication at this time that Brinsley was connected to any terrorist group or organized entity."
He said Brinsley had earlier shot and seriously wounded a woman in Baltimore believed to be his ex-girlfriend. Shaneka Nicole Thompson, 29, was shot in the abdomen, Baltimore authorities reported. She is in critical but stable condition at a hospital and investigators hope to be able to interview her.
The two police department discussed an Instagram post, allegedly by Brinsley, that read, I'm Putting Wings On Pigs Today. They Take 1 Of Ours, Let's Take 2 of Theirs. The posting made reference to high-profile deaths of African-Americans Micheal Bown and Eric Garner." Police officers killed both of them.
Liu and Ramos "will be remembered." he wrote. "They will join a line that is too long, a line of partners who served together and made the ultimate sacrifice together." The memo then named other officers who have lost their lives. "May God grant Officer Wenjian Liu and Officer Rafael Ramos rest. And to all members of the service, be safe,"
New York Governor Andrew M. Cuomo directed that all flags on state government buildings in New York City be flown at half-staff.
When a police officer is murdered, it tears at the foundation of our society, the mayor said. "It is an attack on the very concept of decency."
President Barrack Obama condemned the shooting and called Bratton on Sunday to express condolences for the slained officers.
"Two brave men won't be going home to their loved ones tonight, and for that, theres is no jurisdiction. Obama said in a statement. "The officers risk their own life to serve and protect our communities every single day - and they deserve our respect and gratitude every day."