In May, Detective Hamdy, a 14-year veteran of the Police Department, helped rescue five people trapped in a burning apartment while executing a warrant in a neighboring building in the Rockaways.

“We were in the right place at the right time,” Detective Hamdy said at the time. He and fellow team members forced their way into the apartment and felt their way along the walls of smoke-filled rooms before coming upon five frightened people, age 8 to 22, in a back bedroom.

Before becoming a police officer, Mr. Hamdy served four years in the Marine Corps, joining in 1992 and rising to the level of sergeant in an artillery division based out of Camp Lejeune, in North Carolina. He performed well there, his military records indicate, earning medals for good behavior and for performing his duties above and beyond what was required.

On Friday evening, Police Commissioner Raymond W. Kelly met with Mr. Polanco’s mother, Cecilia Reyes, for about 15 minutes at her home to express his condolences, according to Paul J. Browne, the Police Department’s chief spokesman.

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Outside Detective Hamdy’s home in Centereach, on Long Island, a beige-and-white ranch with a fenced backyard and a pool, a Suffolk County police car sat idling by the driveway on Friday.

As details about Detective Hamdy’s life and career emerged, Police Department officials were silent Friday about the circumstances of the shooting. The Queens district attorney, Richard A. Brown, issued a statement saying that his office and the Police Department’s Internal Affairs Bureau were investigating it. “The public can be assured that the investigation will be full, fair and complete,” Mr. Brown said.

At 1:30 a.m. on Friday, Ms. Reyes, standing outside Ice NYC, a lounge in Astoria, Queens, where Mr. Polanco worked, struggled to get the words out. She pressed the palm of her hand to her mouth in an attempt to mute her sobs. She used her other hand to wipe her tears.

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“I’m sorry,” she said. “I just lost my son.”

Mr. Polanco’s mother said she did not learn that her son was dead until about 2 p.m. on Thursday, nearly nine hours after the shooting. She was at her job as a clerical assistant at Elmhurst Hospital Center when the police told her, she said.

“They are going to pay for this,” she said. “This is not going to stay like this. They are going to get justice.”

For the relatives and friends who encircled her, Ms. Reyes’s grief needed no explanation.

They lighted candles and placed bouquets of flowers at the base of a traffic light on the corner of 33rd Street and Broadway.

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Photocopied images of Mr. Polanco were taped to a metal pole. The crowd parted and cleared a path for Ms. Reyes. Someone handed her a black marker, which she held aloft and pressed against a photo of her son dressed in Army fatigues. “Mom loves you,” she wrote, adding balloonlike hearts as bookends on either side of those three words.

The events leading to the fatal shooting began about 5:15 a.m. on Thursday, the police said. They said that Mr. Polanco was driving erratically, switching lanes while speeding, and twice cutting off two police trucks carrying nine officers of the Emergency Service Unit, the parent unit of the Tactical Apprehension Team.

The officers, members of the apprehension team, had just executed a warrant in the Bronx and were headed to Brooklyn to execute another warrant, and were traveling eastbound on the parkway near La Guardia Airport, the police said.

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Mr. Polanco had just left Ice NYC, where he worked part time in the hookah lounge, filling and serving tobacco water pipes. Though he was not working, he had gone to the club to give a bartender, Diane Deferrari, and Ms. Deferrari’s friend, Vanessa Rodriguez, an off-duty police officer, a ride home. All three lived near one another in Corona, Queens.

The two police trucks forced Mr. Polanco to stop after one truck went in front of his vehicle, a Honda, while the second one maneuvered behind it.

After the car stopped, along a median of the busy highway, two officers approached the car, a sergeant at the driver’s side and the detective at the passenger side, where the window was open, the police said.Ms. Deferrari later told the police that she had heard the officers order those inside the car to show their hands. In an interview, she said that Mr. Polanco had no time to comply and that, in that instant Detective Hamdy fired the shot. Ms. Deferrari said she believed the shooting was the result of a case of police road rage.

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No weapons were found inside Mr. Polanco’s car, the police said.

Edward Mullins, the president of the Seargents Benevolent Association, said he did not believe that road rage played a role in the shooting. “Do you know the level of stress and training that’s involved with this unit?” Mr. Mullins said. “And for officers to lose it over a road-rage incident? That doesn’t make sense. These are not rookie cops. These are experienced, veteran police officers who are used to being under heavy, stressful situations.”

Michael Palladino, president of the Detectives’ Endowment Association, the union that represents Detective Hamdy and other detectives, characterized the bartender’s version of events as “absurd.”

“No police officer would shoot a person who has both hands on the steering wheel,” Mr. Palladino said Friday night. “We have gone done this road before so I ask the public to withhold their judgment until the investigation is complete.”

On Friday afternoon, at the sprawling LeFrak City complex, where Mr. Polanco lived with his mother, uniformed National Guardsmen who served with him stopped to pay their condolences and offer support for the family. Many in his unit, the 1156th Engineer Company, live nearby, a Guard spokesman said.

Under a warm fall sun, a few stopped to make brief remarks to the reporters at the edge of the development.

Upstairs, relatives comforted Ms. Reyes, spoke to lawyers and planned a Saturday morning news conference that she would hold with the Rev. Al Sharpton. It was the second time this year that the 17th-floor apartment was filled with mourners.

Over the summer, Ms. Reyes’s husband killed himself, and friends said it was Mr. Polanco who found his stepfather dead in the living room.