Ismaaiyl Brinsley Surveillance Video View Full Caption NYPD

ONE POLICE PLAZA — The NYPD is scrambling to fill a nearly three-hour gap in their account of where Ismaaiyl Brinsley was before he fatally shot two police officers at close range in Brooklyn on Saturday.

Detectives culled surveillance video from all over the city, Chief of Detectives Robert Boyce said, but lost track of Brinsley between noon and 2:45 p.m., just before he killed Officers Rafael Ramos, 40, and Wenjian Liu, 32.

The NYPD’s Computer Crimes Squad is in the process of putting together a profile of Brinsley, Boyce said, “and it’s quite scary.”

Detectives also combed through Brinsley’s 119 Instagram posts, where he made threats about killing officers.

Police Track Ismaaiyl Brinsley in Fort Greene or Bed-Stuy View Full Caption

“A lot of these things are self-despair, but they’re also anti-government,” Boyce said. "We have a very disturbed young man here."

Brinsley's threats and actions have also inspired a slew of people, according to NYPD Commissioner Bill Bratton.

"An awful lot of copycat threats have come in the meantime," Bratton told "CBS This Morning" on Tuesday, where he also made his case for the public's help in clarifying Brinsley's whereabouts before the shooting.

Now police are turning to the public for help, with surveillance video showing Brinsley at one of his last known locations.

“We owe it to the family to find out what happened here,” Boyce said, speaking of the families of the murdered officers, as well as Brinsley's family.

Ramos was a father of two teenage boys, and Liu was married just two months ago. Brinsley's mother lives in Brooklyn and said on Monday that she was "horrified" when she learned her son killed two police officers.

Surveillance video recorded inside Atlantic Terminal Mall about noon on Saturday shows Brinsley in a "distinctive" jacket that detectives hope will jog the memory of anyone who saw him. The shopping center is also the last place they were able to trace the phone Brinsley was carrying.

“He dumps the phone and we lose him,” Bratton said in a press briefing at One Police Plaza on Monday.

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Nearly three hours later, Brinsley appears on a Tompkins Avenue store’s exterior surveillance video talking to two men on the street, police officials said.

The men told police on Sunday that Brinsley asked them if they were Crips or Bloods and told them to follow him on Instagram. After that he boasted, “Watch what I’m going to do,” before sauntering over to the officers' vehicle and shooting them.

The two men he spoke with trailed Brinsley from a distance, thinking he was going to the Tompkins Houses to start a fight with someone in a gang. They were horrified by what unfolded, according to NYPD Deputy Commissioner for Public Information Stephen Davis, and told detectives they never expected him to fire four rounds at the two officers sitting in their car.

Because Brinsley talked to the men, detectives believe he might have had conversations with other people in Fort Greene, near Atlantic Terminal, or in Bed-Stuy, that may help police understand “what was going on in his mind through these last few hours of his life” and “flesh out his motivation.”

The terror Brinsley wrought on Saturday began in a suburb outside Baltimore, where he broke into the apartment of his ex-girlfriend, Shaneka Nicole Thompson, wielding a gun.

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“He put the gun to his own head, but she talked him out of that,” Boyce said, describing Thompson as “quite a courageous young woman.”

But Brinsley turned the gun on the woman and shot her in the stomach.

Brinsley took off with Thompson’s cell phone, calling her mother to say he didn’t mean to shoot her daughter, and that he hoped she survives. He also called his own mother at one point, Davis said.

He boarded a BoltBus to New York City, and Baltimore police, knowing he had Thompson’s cell phone, were able to track him along I-95 whenever he used the phone, whether to make a call or use the Internet.

Davis said the NYPD still hasn’t pinpointed exactly which bus Brinsley took, but they have video of him in the subway system at 42nd Street and Eighth Avenue, and again in Brooklyn at Atlantic Terminal.