Holly Yan et al., CNN, December 22, 2014

The cop-killer didn’t seem to have a specific target–just any two officers in uniform.

And on the day of his deadly attack, those officers just happened to be Wenjian Liu and Rafael Ramos.

While patrolling a Brooklyn neighborhood Saturday, the New York police officers were killed by the man who had also just shot his ex-girlfriend–and apparently broadcast his intention to kill police on social media.

Here’s what we know about the shooting, the victims and the latest threats against police:

The attack

Liu and Ramos were sitting in their patrol car in a high-crime part of Brooklyn when–without warning–the gunman shot them in the head.

“They were, quite simply, assassinated,” New York City Police Commissioner William Bratton said.

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Police said the shooter was 28-year-old Ismaaiyl Brinsley. Hours before he killed Liu and Ramos, Brinsley shot his ex-girlfriend near Baltimore. The woman, 29-year-old Shaneka Nicole Thompson, was shot in the stomach but survived.

A series of social media posts believed to be from Brinsley gave ominous clues that police would be next.

The warnings

It was one of the ex-girlfriend’s friends who alerted Baltimore County Police to troubling Instagram posts that the friend believed came from Brinsley.

“These posts included overt threats to kill police officers,” police said. And they appeared to be posted in Brooklyn, New York.

“I’m Putting Wings On Pigs Today,” one Instagram post read, according to police. “They Take 1 Of Ours, Let’s Take 2 of Theirs.”

Brinsley also posted messages of self-loathing and despair and made reference online to Michael Brown and Eric Garner, black men who were killed by police.

Around 2:10 p.m., 40 minutes after speaking with the friend, Baltimore County police said they called New York police to warn them. Then they faxed a “wanted” poster with Brinsley’s picture.

“Suspect is armed with a 9mm handgun and has posted pictures on Instagram saying that he will shoot a police officer today,” a description on the flier says.

But it was too late. New York Police Chief of Detectives Robert Boyce said while New York police were spreading the warning, Brinsley ambushed and killed the two officers.

Later, at a nearby subway station, Brinsley was found dead of a self-inflicted gunshot wound.

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As they grieve the deaths of two of their colleagues, New York police must also deal with a spate of new threats.

The NYPD is investigating more than 15 threats to officers posted on various social media platforms and trying to determine whether any are serious or credible, a senior New York City law enforcement officer told CNN.

The department’s intelligence division continues to monitor social media for threats made to the NYPD. Officials have not released details about any potentially credible threats.

But the troubling messages aren’t just coming from New York.

A Memphis, Tennessee, man has been questioned after allegedly posting threats against the NYPD, CNN affiliate WREG reported.

“Good job. Kill em all I’m on the way to NY now #shootthepolice 2 more going down tomorrow,” an Instagram post read.

The NYPD has already pulled all of its auxiliary officers off the streets in the wake of the killings of the two officers. Auxiliary officers are unarmed volunteer officers who help with traffic control or other minor situations.

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