A New York police detective shot and killed an unarmed man, whose hands, a witness said, were on the steering wheel of his Honda, after he had been pulled over early Thursday for cutting off two police trucks on the Grand Central Parkway in Queens, the authorities said.

The shooting, which occurred at 5:15 a.m., was the latest in a series of episodes in which police officers fatally shot or wounded civilians. While the Police Department had explanations in the other instances, it could not immediately provide one for the shooting on Thursday.

The detective, Hassan Hamdy, 39, a 14-year veteran assigned to the Emergency Service Unit, fired one bullet through an open window of the car, which his squad had just pulled over with the help of a second police vehicle. The bullet struck the driver, Noel Polanco, 22, in the abdomen. He was declared dead less than an hour later at New York Hospital Queens.

Paul J. Browne, the department’s chief spokesman, initially said there were reports of movement inside the car, although he did not elaborate. Mr. Browne said a small power drill was found on the floor on the driver’s side, but he later appeared to play down the importance of that information.