Two NYPD police officers were ambushed and slain "execution style" Saturday.

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Police guard the scene where two NYPD officers were shot, Saturday, Dec. 20, 2014, in New York. An armed man walked up to two New York Police Department officers sitting inside a patrol car and opened fire Saturday afternoon, killing one and critically wounding a second before running into a nearby subway station and committing suicide, police said. (AP Photo/John Minchillo)

The lone gunman who walked up to a Brooklyn patrol car and opened fire, killing two New York City police officers, has been identified as a Balitmore man who posted chilling anti-cop messages to social media Saturday before driving up to New York to carry out his threats.

New York City Police Commissioner Bill Bratton, speaking at a press conference Saturday night, confirmed the identity of the shooter as 28-year-old Ismaaiyl Brinsley. He also identified the two slain cops as Wenjian Liu and Raphael Ramos.

According to Balitmore police, Brinsley shot and wounded his girlfriend there earlier Saturday before traveling to Brooklyn, Bratton said. The woman's mother contacted New York City police, to warn them of Brinsley's plans, but the message came too late to save the two cops.

Bratton said Brinsley took a shooting stance on the passenger side of the police cruiser and fired several times striking both officers in the head. The pair, he said, never had the chance to draw their own weapons and may never have seen their assailant.

“Both officers paid the ultimate sacrifice today,” Bratton said.

New York City Mayor Bill de Blasio, speaking after the commissioner, called the attack an "assassination" and said that when a police officer is attacked, every New Yorker should feel as though they were attacked, too.

“Although we are still learning the details, it’s clear that this was an assassination. These officers were shot execution style,” de Blasio said. “A particularly despicable act … when a police officer is murdered, it tears at the very foundation of our society.”

"Our city is in mourning, our hearts are heavy," he said.

The mayor had been critcized recently by New York City police union leaders for comments percieved as unsupportive of the city's police force after an officer investigated in the chokehold death of Staten Island man Eric Garner was not indicted.

The New York Daily News, first to identify Brinsley, posted an image of a silver handgun from an Instagram account alleged to be Brinsley's in which he bragged about his plan to kill police officers and indicated the act would be retribution for the police-involved deaths of Ferguson teen Michael Brown and Garner.

The Intsagram caption reads, “I’m Putting Wings On Pigs Today. They Take 1 Of Ours...Let’s Take 2 of Theirs." The account has since been taken down.

Police say the suspect fled to a nearby subway station where he fatally shot himself.

Tensions have run high in the wake of the grand jury decisions in the Brown and Garner cases. In each case, black men were killed by white police officers and the cops investigated were not indicted. There have been protests in New York City almost nightly since the Ferguson decision on Nov. 24.

Saturday's ambush took place about 3 p.m. in Brooklyn's Bedford Stuyvesant neighborhood.

New Yorkers throughout the five boroughs turned to social media to voice their shock and ongoing frustration.

Sabrina de la Torre, who lives in the neighborhood, said she was listening to Christmas music while waiting for the G subway heading to Williamsburg for work, when roughly 20 cops ran onto the platform and screamed for everyone to get down.

“Everyone was very freaked out,” she told Yahoo News. “It was really intense and scary because no one know what was going on. It was a really intense.”

As they ducked down to the ground, de la Torre’s friend John shot a video which she then posted to her Instagram page. The view is clearly from the ground and the feet of several cops are seen rushing by in pursuit of the shooter.

“They kept us kind of detained for a while before we found out anyone was shot,” she said.

About an hour after the shooting, LaBasia McBride posted a video on Facebook showing police officers, medical personnel, and crowds gathering near the shooting site.

“This is crazy. Two cops got shot in the head,” a woman can be heard saying in the clip. “Yes, both of them were shot in the head… that’s crazy!”

Another woman, Jennifer Connic, posted a video to Instagram showing the commotion at the intersection and a helicopter hovering overhead.

Rev. Al Sharpton, a Brooklyn native, who has taken a prominent role in the protests, condemned the attack on Twitter and reiterated his belief in non-violence.

Sharpton also released a statement, obtained by Mediaite, saying that the Garner family is outraged by the police 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 reads.

City Councilman Robert Cornegy, who represents Crowns Heights and Bedford Stuyvesant, said the officers were patrolling public housing complexes as part of a program to increase police presence, DNA Info reports.

"They were just a presence, they weren't over-policing," he said, according to the news site. "They were here as a presence to make the community feel safer."

Many people throughout the country took to Twitter to express deep appreciate for police in the aftermath of the shooting.

The AP contributed to this report.