A two-time convict who has voiced anger at law enforcement officers in the past shot and killed a New York City officer through a police vehicle window in the Bronx early Wednesday, in what the police commissioner called an “unprovoked attack.” The gunman was killed by other officers, the police said.

The officer, Miosotis Familia, 48, was taken to St. Barnabas Hospital, where she was pronounced dead about three hours after the shooting.

The gunman, identified by the police as Alexander Bonds, 34, was paroled in May 2013 after serving seven years in one of New York State’s most notorious prisons for a robbery in the Syracuse area.

In a video he posted to Facebook in September of last year, he railed against prison conditions and warned people of officers raping or killing inmates. But he also hinted that he would not back down in any future confrontations with police officers on the streets.

“I’m not playing, mister officer,” he says into the camera. “I don’t care about 100 police watching this.”

                                                                   Officer, Miosotis Familia,

He added, “I got broken ribs for a reason, son, we gonna shake. We gonna do something. We can’t be dying for free, getting raped for free, just for them to give you hush money. Is you stupid? I don’t want the money. I want justice.”

At another point, Mr. Bonds alluded to encountering officers and said, “I’m not hesitating. It ain’t happening. I wasn’t a bitch in jail and I’m not going to be a bitch in these streets.”

A law enforcement official said detectives have reviewed the Facebook video.

Mr. Bonds, who also went by the name John Bonds, was also convicted in 2004 of criminal sale of a controlled substance near a school, a felony, state prison records indicate. He was sentenced to two to six years in prison.

His attack came at the close of Fourth of July celebrations; several witnesses said they had been setting off fireworks when the police suddenly swarmed the area. It immediately revived memories of ambush-style killings of police officers, including in Brooklyn in 2014 and in Iowa last year.

Officer Familia, who was in uniform, had been sitting in a mobile command unit — a truck-size police vehicle that is big enough to house equipment and several officers — on the south side of East 183rd Street, near Creston Avenue, in the Fordham Heights neighborhood.

Around 12:30 a.m., as Officer Familia neared the end of her shift, Mr. Bonds walked up to the vehicle and fired a single round from a .38-caliber, five-shot Ruger revolver through a passenger-side window, according to Deputy Chief Jason Wilcox, the commander of detectives in the Bronx.

Immediately after the shooting, Officer Familia’s partner, Vincent Maher, called for assistance, and two other officers encountered the suspect, who was running on Morris Avenue, about one block away. When the gunman drew a silver revolver, they opened fire, killing him.

A bystander was struck by a bullet in that shootout, and is in stable condition, said the police commissioner, James P. O’Neill.

“Based on what we know right now, this was an unprovoked attack against police officers who want to keep this great city safe,” Commissioner O’Neill said at a news conference at the hospital, where Officer Familia was pronounced dead at 3:37 a.m. Outside, a line of officers saluted their fallen colleague; some escorted her body to the medical examiner’s officer.

Mayor Bill de Blasio, speaking at the same news conference, praised Officer Familia and expressed the city’s grief.

“She was on duty, serving this city, protecting people, doing what she believed in and doing the job she loved,” he said. “And after this shocking and sudden attack, her fellow officers came to her aid immediately.”

A friend of Mr. Bonds, Elaine Lucas, said in an interview on Wednesday that she had never heard Mr. Bonds voice anti-police sentiment.

“He was a sweetheart,” she said. “A little hardheaded, but a sweetheart.”

She said he had been in and out of homeless shelters and that she had never known him to be violent.

Officer Familia was a 12-year veteran of the police force, assigned to a plainclothes street crime unit of the 46th Precinct.

Chief Wilcox, asked whether the attack could be characterized as an assassination, replied, “Everything is pointing to that.”

At one point, Mr. Bonds lived at a homeless shelter on East 53rd Street in Manhattan, but he lived more recently in the Bronx. A police spokesman said there was no indication that Mr. Bonds had known Officer Familia.

A police vehicle sat in front of Mr. Bonds’s apartment building, on the Rev. James A. Polite Avenue, on Wednesday morning.

A neighbor, Marta Perez, 29, a stay-at-home mom, said the suspect had moved into a second-floor apartment with his girlfriend about five months ago. Police officers flooded the block around 3 a.m., she said, and took his girlfriend in for questioning.