Standing on a sidewalk in Queens, Cecilia Reyes, 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.


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


For the relatives and friends who encircled her at 1:30 a.m. on Friday - less than 24 hours after a police detective shot and killed her son, Noel Polanco, during a traffic stop on the Grand Central Parkway in Queens - her grief needed no explanation.


They had gathered outside the lounge in Astoria, Queens, where Mr. Polanco, 22, had worked to offer their support. They lighted candles and placed bouquets of flowers at the base of a traffic light on the corner of 33rd Street and Broadway. 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 balloon-like hearts as bookends on either side of those three words.


On Thursday at about 5:15 a.m., the police said, Mr. Polanco was driving erratically on the Grand Central, switching lanes while speeding, and twice cutting off two police trucks carrying several officers with the Emergency Service Unit. The officers, members of the unit’s 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.


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 pick up a bartender, Diane Deferrari, and Ms. Deferrari’s friend, Vanessa Rodriguez, an off-duty police officer. Mr. Polanco offered to drive the two women home in his Honda. All three lived near one another in an apartment complex in Corona.


The two police trucks forced Mr. Polanco to stop after one truck went in front of the Honda while the second truck maneuvered behind. 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’s side where the windows were 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, the detective, Hassan Hamdy, 39, fired the shot. Ms. Deferrari said she believed the shooting was the result of a case of police road rage.


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


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


On Friday morning, Ms. Reyes said no one from the Police Department had reached out to her to explain what happened or to express condolences. Her emotions cast a wide pendulum, swinging from anger to anguish.


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


Mr. Polanco’s younger sister, Amanda, 15, who accompanied her mother to the lounge early Friday, said she had faith that the justice system would work.


The shooting is under investigation by the Police Department and the Queens district attorney’s office, which is routine practice for all police-involved shootings.


Ms. Reyes, 46, said that her son would never harm anyone and that she was certain he posed no threat to the officers. Mr. Polanco was a member of the Army National Guard and was assigned to a company headquartered in Kingston, N.Y.


“They are trying to make him look like he was a bad person, but that’s not going to happen,” she said. “I’m going to make sure that his name does not get taken down in the mud.”


She added: “This is my son. This is my life. I don’t know how they could have not thought about that.”


The shooting was the latest in a series of encounters in which police officers have shot or wounded civilians. The killing of Mr. Polanco was different because, so far, the police have not been able to provide an explanation about what prompted Detective Hamdy to fire his gun.


“We want the truth. We want the honest truth,” said Joseph Thomas, 26, one of Mr. Polanco’s friends who joined the crowd outside the lounge in Astoria.


“No one feels safe,” Mr. Thomas added. “This isn’t the first time in which an innocent young man was gunned down. How are they protecting us when they are gunning us down? They are out here shooting us.”


One woman, Claudia Gonzalez, 46, said Mr. Polanco had worked for her providing security at a dance hall she operated in Corona. But he left his job with her, she said, because he thought it was too dangerous and he did not like to break up fights.


“I know a list of kids that I could say, ‘O.K., he had it coming; he didn’t listen.’ Not Noel,” she said. “Innocent blood was truly shed here.”