Video Shows Aftermath of Two Police Officers Gunned Down in Cold Blood

Police leaders across the country issue warnings for officers as anti-government sentiment raises safety concerns.
3:48 | 12/23/14

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Transcript for Video Shows Aftermath of Two Police Officers Gunned Down in Cold Blood
But first, the breaking developments tonight. The new video coming in after those two New York City police officers were murdered in cold blood. Ambushed as they sat in their police car. The new images minutes after gunshots rang out. You can see there at the bottom of your screen. One of the officers on that stretcher. Tonight, authorities are studying this new surveillance tape. The suspect in the hours before. The weapon, they believe, inside that bag. Tonight, the new alerts going out in cities across this country to keep their officers safe. ABC's linsey Davis with the new surveillance tonight. Reporter: Tonight, these new images of the moment of crisis. A cop got hot! Reporter: Police swarming the scene, rushing to an ambulance one of the two Brooklyn police officers gunned down Saturday in broad daylight by a man authorities have identified as 28-year-old ismaaiyl brinsley. Poilce say brinsley was on a mission to kill cops. That morning he left Baltimore after allegedly shooting his ex-girlfirend. Arriving in New York before noon, on a bus. Police releasing this video of brinsley at a Brooklyn mall, his gun, they say, in that bag. Baltimore detectives soon discovering threats he posted on instagram. "I'm putting wings on pigs today. They take one of ours, let's take two of theirs." With the hashtag shoot the police, rip Eric garner and rip Mike brown. They alerted the NYPD, but word never got to officers wenjian liu and Rafael Ramos, sitting in their patrol car in Brooklyn. 2:47 P.M., police say brinsley approached that car, telling bystanders "Watch what I'm about to do." He walked up to the passenger side and fired four shots, striking both officers in the head. Shots fired. Shots fired. Reporter: As police descended, the gunman fled. S.w.a.t. Teams chased the suspect here to this nearby subway station. Police say brinsley then shot himself in the head. Tonight, a city in mourning. Officer liu leaves behind a wife of just two months. Officer Ramos, two sons. His 13-year-old writing on Facebook, 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. Many in the NYPD now angry with New York mayor bill de Blasio, who they say has been too impathetic to anti-police protesters. Today, de Blasio calling for calm. The assassination of these two officers was an attack on the city of New York as a whole, on every one of us, on our values, on our democracy. We cannot tolerate such attacks. Reporter: Tonight, the mayor asking that all police protests be put on hold until after the officers unirals. Officer Ramos is scheduled to be laid to rest on Saturday. This memorial only continues to grow. Linsey Davis live in Brooklyn tonight. Thank you. Let's get right to Pierre Thomas tonight, and Pierre, several cities putting out alerts and you have some of them tonight? Reporter: That's right, David. Not just in New York, but in the Atlanta suburbs, Boston, Baltimore, New Jersey, Pittsburgh and other locations across the country. Police leaders and unions have issued warnings urging extra caution. In short, telling their running and file they could be targeted and ambushed. In a number of cases, officers are being told not to go on patrols alone, be extra careful about their surroundings and be cautious about what they post on social media. Even before that scene here in New York this weekend, this has been a dangerous year for police across the country? Reporter: Police deaths have been spiking compared to 2013, David. The number of officers killed in the line of duty has surged by 23%, with those killed by firearms up 58%. Authorities say there's a lot of anti-government, anti-police sentiment out there right now. All right, Pierre Thomas live in our Washington bureau, Pierre, thank you.

This transcript has been automatically generated and may not be 100% accurate.

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