— -- An on-duty New York City police officer was killed early Wednesday after a gunman walked up to a police vehicle and fired one round through a window, authorities said.
Officer Miosotis Familia, a 12-year veteran assigned to the New York City Police Department's 46th Precinct's anti-crime unit, was taken to St. Barnabas Hospital in the Bronx, where she was pronounced dead at 3:37 a.m. ET. She was 48 years old, according to police sources.
At a press conference Wednesday morning, New York City Police Commissioner James P. O'Neill said Familia was shot in the head in an "unprovoked attack" while sitting with her partner in a marked police command vehicle on the corner of Morris Avenue and East 183 Street in the Bronx around 12:30 a.m. He told reporters the vehicle had been parked there since March because of increased gang activity in the area.
Familia's partner radioed for assistance while other uniformed officers chased after the suspect, who took off on foot. As the officers confronted the suspect, he drew a revolver, and the officers shot and killed him, according to O'Neill.
The shooter has since been identified as Alexander Bonds, 34, of New York City. The .38 caliber revolver recovered from the crime scene was stolen in West Virginia in 2013, police sources told ABC News.
Another person, believed to be an innocent bystander, was struck by a bullet during the confrontation. The individual was hospitalized with non-life-threatening injuries, according to O'Neill.
Familia's partner was not injured in the attack.
"It is clear this was an unprovoked attack on police officers who were assigned to keep the people of this great city safe," O'Neill told reporters at St. Barnabas Hospital. "She was sitting in the vehicle, and he came up and fired a round into the vehicle. I don't know if anything else could be more unprovoked than that."
O'Neill noted that the area where the shooting took place has been troubled by gun violence and gang activity.
He later wrote on his verified Twitter account that Familia was "assassinated."
A police source told ABC News that surveillance footage recovered from the scene shows the suspect "purposefully" walking up to the command vehicle and firing into the passenger's side window. Familia was writing in her memo book at the time, indicating that she may not have seen the suspect approach, police sources said.
In an internal memo to staff, O'Neill wrote that Familia's death was a "direct attack on police officers assigned to safeguard the people of New York City" and that she was "murdered for her uniform and for the responsibility she embraced."
"For nearly 12 years, Officer Familia did what each of you also swore an oath to do every day, on every tour: fight crime and disorder, and improve people’s lives," O'Neill wrote. "Officer Familia dutifully lived up to that promise because she believed, as each of you do, that the safest big city in the nation can become even safer."
New York Gov. Andrew Cuomo announced Wednesday that flags at all State government buildings will be flown at half-staff Thursday to honor Familia.
"Law enforcement officers across New York put their lives on the line to protect and serve their communities," Cuomo said in a statement. "This horrific and senseless assassination is a devastating reminder of the risks these brave men and women face each day."
New York Mayor Bill de Blasio's press secretary said he was briefed on the matter and visited St. Barnabas Hospital.
Patrick J. Lynch, the president of the Patrolmen's Benevolent Association, New York City police officers' union, said Familia was a mother of three who "gave her life protecting a neighborhood that had been plagued by gang gun violence."
"Fully knowing the dangers that she faced, she suited up in uniform every day and stood tall against those who threaten and terrorize the good folks of the Bronx," Lynch told reporters at Wednesday morning's press conference.
Lynch urged the public to be on the lookout for anti-police activity in the area near Familia's murder.
"This kind of violence against police officers cannot stand. We need the public's help," he said. "When you see someone that's making threats, doing something against police officers, you need to let us know. You need to be our eyes and ears."
ABC News' Matt Foster, Aaron Katersky and Rachel Katz contributed to this report.