A police officer was suspended without pay Monday after the fatal shooting of an unarmed driver who may have pretended to have a gun during a traffic altercation a day earlier, when the officer was off-duty.

The undercover narcotics officer turned himself in Monday, said Police Commissioner Raymond Kelly. His gun was taken from him pending possible action by the prosecutor's office, police said.

The 34-year-old was not arrested and has been released, but authorities said criminal charges against him were possible. The Manhattan district attorney's office was investigating, said spokeswoman Barbara Thompson. His name was not released.

The officer, who has been with the force since 2004, was involved in a traffic dispute that began early Sunday after a fatal motorcycle accident forced police to divert traffic off the FDR Drive in East Harlem, police said.

Jayson Tirado, 26, apparently refused to let the narcotics officer's sport utility vehicle merge into traffic, and "words were exchanged," Police Commissioner Raymond Kelly said.

A passenger in Tirado's car told police that Tirado "made reference to the fact that he had a gun — 'Mr. Ruger' or something like that" — then pointed toward the officer with his right index finger, Kelly said.

At least one shot struck Tirado in the torso, and he died at a hospital, Kelly said.

The officer left the scene but approached a marked police car early Monday, identified himself, said he was having chest pains and "then makes a statement he may have shot somebody," Kelly said.