NEW YORK (CBSNewYork) – The NYPD has shed more light on the events that led up to the execution of two NYPD officers in Brooklyn on Saturday.

New York City Chief of Detectives Robert Boyce said the man behind the killings, 28-year-old Ismaaiyl Brinsley, was born in Brooklyn and has a mother who lives in the borough.

But Brinsley actually began his crime spree in Baltimore, Maryland.

According to Boyce, Brinsley went to the home of a former girlfriend in Baltimore around 5:30 a.m.

As 1010 WINS’ Derricke Dennis reported, Brinsley used an unauthorized key to gain entry and a confrontation broke out before he shot her in the abdomen. She is expected to survive.

Brinsley then took her phone and fled, Boyce said.

“At about 6:05 in the morning he calls the mother on her phone, the girlfriend’s mother on the phone, and he says he shot her by accident and that he hope she lives,” Boyce said.

Police in Baltimore said they noticed Brinsley posting to the woman’s Instagram account about a threat to New York officers as they tracked his movements.

Boyce said Brinsley arrived in New York City around 10:50 a.m. and discarded the woman’s cell phone near the Barclays Center just after 12 p.m.

According to Police Commissioner Bill Bratton, Baltimore authorities sent a wanted flier between 1:30 and 2 p.m. to the NYPD and other agencies following the shooting in Baltimore, warning them of Brinsley. Bratton said it was sent at essentially the same time the officers, 40-year-old Rafael Ramos and 32-year-old Wenjian Liu, were being ambushed by the suspect.

Bratton said Brinsley traveled to Bedford-Stuyvesant and “ambushed and murdered” the two officers as they sat in their marked police car.

Just before the shooting, Boyce said Brinsley spoke with witnesses and said, “Watch what I’m going to do.” He also asked if they had any gang affiliation and said to follow him on Instagram, according to Boyce.

Bratton said Brinsley then approached the passenger window of the police car and opened fire, striking the two in the head.

Cell phone video taken from an apartment window shows EMTs trying to save the lives of the officers, CBS2’s Matt Kozar reported.

Brinsley then fled toward a nearby subway station and Boyce said two Con Ed workers who witnessed the shooting gave chase in their truck before flagging down other officers in the 75th Precinct.

Those officers were able to pursue Brinsley to the subway station where he fatally shot himself in the head, Boyce said.

A silver semi-automatic firearm was recovered at the scene.

Boyce said there were a total of 10 witnesses to the shooting, as well as another 10 witnesses at the subway platform where Brinsley took his life.

Police are also analyzing five surveillance videos from the two scenes, two of which are before the shooting, two after the shooting and one from the subway station. Boyce said there is no known surveillance video that depicts the homicide.

As the investigation into a motive continues, Boyce said they’ve learned more about the suspect through his Facebook account, Instagram, Gmail and two phones that were recovered — his ex-girlfriend’s and a private phone recovered in Baltimore.

Boyce said Brinsley expressed anger at the government and in one online posting burned an American flag. He also talked of anger at police and mentioned the Eric Garner and Michael Brown cases, Boyce said.

Brinsley appears to have no gang affiliation and no religious statements were made on his social media accounts, Boyce added. Brinsley’s family is Muslim, but Boyce said his family told police he never expressed any statements suggesting religious radicalization.

The NYPD said Brinsley’s last known address was in Georgia, but that he had not been to the residence in nearly two years and was estranged from his sister who lived there.

Brinsley’s mother told police he had a violent childhood and police said he was suicidal and tried to hang himself a year ago. Though, it’s not clear if he was ever diagnosed with a mental illness.

Investigators said Brinsley was in New York City a week ago and are looking into whether he was invoved in any of the rallies and protests. He has no prior arrests in New York City, despite family ties to the city, police said.

Brinsley’s past criminal record in Georgia, beginning in 2004, ranges from simple battery to trespassing to carrying a concealed weapon in 2007.

Cobb County court records show Brinsley was also charged July 2011 with possession of a firearm by a convicted felon as well as discharging a firearm, along with a myriad of other charges.

Baltimore Mayor Stephanie Rawlings-Blake said in a statement on Saturday she is troubled to learn Brinsley started his crime spree in her community, WNEW’s Heather Curtis reported.

Rawlings-Blake’s deputy chief of staff, Kevin Harris, said the mayor knows there are a few bad apples that have “done some things that do not honor the uniform,” and they need to deal with that.

“But the way in which they do that is not to target law enforcement,” Harris told Curtis.

On Sunday, Rawlings-Blake called the shootings “an act of cowardice.”

“…And in no way honors the lives lost in police custody, nor does this heinous act represent the overall views of those who have protested peacefully against police misconduct,” Rawlings-Blake said.

The NYPD will continue to work with Baltimore authorities to determine a motive of what brought Brinsley to Brooklyn, Bratton said.

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