New York (CNN) -- The man who shot and killed two New York City police officers as they sat in their patrol car had posted angry messages on social media, ranting against the government and police, New York Police Department's Chief of Detectives Robert Boyce said Sunday.
"I'm Putting Wings On Pigs Today. They Take 1 Of Ours, Let's Take 2 of Theirs," an Instagram post read, authorities said.
Brinsley had a lengthy criminal record. He was arrested 15 times in Georgia for assorted crimes and arrested four times in Ohio, Boyce told reporters Sunday.
He was in prison in Georgia between August 2011 and July 2013 for criminal possession of a weapon, Boyce said.
Brinsley had an address connected to him in Georgia but that appears to be his sister's home, and they are estranged, Boyce said. The gunman's connection to Brooklyn is that his mother lives there, but they are also estranged, the chief of detectives said.
On Saturday afternoon, Brinsley fired four rounds at officers Rafael Ramos and Wenjian Liu in the Bedford-Stuyvesant neighborhood. The officers, who were hit in head, were assigned from their normal downtown Brooklyn beat to an area of the borough with a high crime rate, authorities said.
New York City Police Commissioner William Bratton said the officers were shot "with no warning, no provocation."
Witnesses saw Brinsley walk to the car and assume what they described as a shooting stance.
"They were, quite simply, assassinated," Bratton said.
At a nearby subway station, Brinsley was found dead of a self-inflicted gunshot wound, authorities said.
A message from a teenage son of Ramos' showed the heartbreaking devastation the crime has caused.
"Today is the worst day of my life," 13-year-old Jaden Ramos posted on Facebook about the slaying of his father, Rafael Ramos.
"Today I had to say bye to my father," the teenager wrote. "He 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 says they hate cops but they are the people that they call for help. I will always love you and I will never forget you. RIP Dad."
The thin blue line
Family and friends of Ramos spoke to reporters Sunday, expressing support for police and a desire for change.
"We're just hopeful that this tragedy will not be in vain and that we will be able to heed the words of the Ramos family and bring the city together to heal," said U.S. Rep. Hakeem Jeffries, a Democrat who represents large sections of Brooklyn.
Ramos had just turned 40; Liu had been married two months ago.
Both had dreamed of being police officers, Bratton said.
"One of the unfortunate realities of policing is that you put that blue uniform on and you become part of the thin blue line between us and anarchy," Bratton said.
He sent a memo to NYPD officers about the killings, saying the officers were "targeted for their uniform, and for the responsibility they embraced: to keep the people of this city safe."
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," he said.
New York Gov. Andrew M. Cuomo directed that all flags on state government buildings in New York City be flown at half-staff.
Mayor Bill de Blasio and Bratton met with the families of the victims.
"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 Barack Obama condemned the shooting, and called Bratton on Sunday to express condolences for the slain officers.
"Two brave men won't be going home to their loved ones tonight, and for that, there is no justification," Obama said in a statement. "The officers who serve and protect our communities risk their own safety for ours every single day -- and they deserve our respect and gratitude every single day."
U.S. Attorney General Eric Holder called the attack "an unspeakable act of barbarism."
The suspect and his lethal travels
Brinsley arrived in New York from Baltimore but had a home in the Atlanta suburb of Union City, Georgia.
Boyce said that there is no indication that Brinsley had any gang ties, and police have found no religious statements on social media accounts that investigators continue to pour through.
Before he arrived in Brooklyn by bus, Brinsley had shot and seriously wounded an ex-girlfriend in Baltimore on Saturday morning, Boyce said. Shaneka Nicole Thompson, 29, was shot in the abdomen, Baltimore authorities said Sunday.
She is in critical but stable condition at a hospital, authorities told CNN. Investigators were able to talk to her, Boyce said. She said that when Brinsley showed up at her apartment, they argued. Her mother called during that and heard the bickering but the phone hung up, according to Boyce. The first call to 911 came at 5:50 a.m. from a neighbor who heard shots fired.
Brinsley later called the mother back and apologized for shooting her daughter, saying it was an accident and that he hoped she lived, Boyce said.
Baltimore authorities communicated to New York police Sunday at about 2:10 p.m. when Baltimore County police made a phone call to the 70th Precinct in New York to tell police there that the phone of a suspect wanted in Thompson's shooting was pinging at a location in the 70th Precinct.
The two police departments discussed an Instagram post, allegedly by Brinsley, that read, "I'm Putting Wings On Pigs Today." The posting made reference, police said, to the high-profile deaths of African-Americans Michael Brown and Eric Garner. Police officers killed both men.
"They Take 1 Of Ours, Let's Take 2 of Theirs," the post said, according to authorities. The account also displayed a handgun and a message that said it might be the poster's last message.
Baltimore County police also faxed a "wanted" poster to New York police with information about Brinsley.
Records show Brinsley had a lengthy arrest record in Georgia, mostly involving charges of shoplifting and illegal weapons possession, records show.
He was also charged with property damage and obstructing a police officer and pleaded guilty to many of the charges, according to police and court records.
Reaction: 'This can't happen'
The shooting shocked residents in the neighborhood.
"This can't happen. If you mad at somebody, be mad at the person that you are mad at. Now, we have two families that (are) missing somebody for the holidays," Shaniqua Pervis told CNN affiliate WABC.
"Where is your humanity? I know it's a war going on and shoutout to Eric Garner's family and everybody else who lost somebody, but you're not at his house, on his lawn. This is two (officers). You don't even know if (they were) good or bad. I don't condone this, and I'm not with it."
The woman was referring to the controversial July death of the unarmed black man after New York police officers on Staten Island wrestled him to the ground, with one of the officers wrapping his arm around Garner's neck in a chokehold.
A grand jury's decision not to indict the police officer in the Garner case, as well as a separate grand jury's refusal to indict an officer in a controversial police shooting of unarmed teen Michael Brown in Ferguson, Missouri, led to nationwide protests against the police.
Brown's family condemned Saturday's slayings.
"We reject any kind of violence directed toward members of law enforcement. It cannot be tolerated. We must work together to bring peace to our communities," they said in a statement.
"Our thoughts and prayers go out to the officers' families during this incredibly difficult time."
In a statement, activist the Rev. Al Sharpton said the Garner family was outraged by the police officers' killings.
"Any use of the names of Eric Garner and Michael Brown, in connection with any violence or killing of police, is reprehensible and against the pursuit of justice in both cases," the statement said. "We have stressed at every rally and march that anyone engaged in any violence is an enemy to the pursuit of justice for Eric Garner and Michael Brown."
Tensions between the community and police have heightened around the country since the deaths of Brown and Garner.
"This could not have come at a worse time," City Councilman Robert Cornegy told CNN affiliate WPIX.
CNN's Ray Sanchez, David Shortell, Mariano Castillo and Kevin Liptak contributed to this report.