Nassau County police were refusing to discuss the circumstances of the shooting, but were expected to issue a statement later Tuesday.
A law enforcement official confirmed that the Nassau County officer and a civilian were killed near the Cross Island Parkway in Bellerose Terrace, a community at the Queens-Nassau border. The official wasn't authorized to discuss the investigation and spoke to The Associated Press on condition of anonymity.
New York City Police Commissioner Raymond Kelly said investigators were trying to sort out what happened. He said the shooting occurred after police stopped a driver for leaving the scene of an accident. Investigators suspect the driver may have left the scene and shot another person a short distance away, Kelly said.
"We found a body there with a bullet wound to the head," he said.
A man who said he witnessed the shooting of the officer while the man was stopped at a gas station along the highway said it looked like a routine traffic stop.
"The officer's walking up to the car. They just pulled out (a gun) and shot," said Paul Walcott, a music producer from Bayside, Queens. "He went right down. He got hit point blank. He went straight down."
The car then sped off, heading south on the Cross Island Parkway.
"In broad daylight, this time of day, it was incredible to see something like that," Walcott said.
It was the second time in the past week that a Nassau County officer has died in the line of duty.
Highway patrolman Joseph Olivieri was killed Thursday while responding to a traffic accident caused by an alleged drunken driver. The driver, who was later charged with DWI smashed into one car, then drove on a short distance before stopping. A car then hit that driver's vehicle, turning it sideways in the road. The police officer who arrived to investigate was then struck by an SUV that happened upon the crash scene.
Thousands of police officers attended a funeral Monday for Olivieri outside a Long Island church.