The detective, who was off duty at the time and whose name had not yet not yet been released on Tuesday, previously told detectives and his lawyer that while he had followed the motorcyclists from the Henry Hudson Parkway onto a Washington Heights street, he left the scene once some of the riders began attacking the vehicle.
But investigators found his story suspicious from the beginning — in part because the detective took several days to come forward after the violent and chaotic episode on Sept. 29, said the official, who spoke only on the condition of anonymity because the charges had not yet been formally filed. The official would not provide the name of the detective.
The detective's story was contradicted, the official said, by video taken at the scene and obtained by the police and prosecutors, as well as by witness statements. In the video, the detective can be seen pounding his fists into the back of the vehicle.
It was not immediately clear whether the detective struck the driver, Alexian Lien, 33, after he was pulled from the black Range Rover by other motorcyclists in traffic on 178th Street in Washington Heights, the official said.
"He's arrested," said Philip E. Karasyk, a lawyer for the Detectives Endowment Association who is representing the detective. The detective was placed on modified duty after he came forward last Wednesday — three days after the episode — to say he had been present. His arrest will automatically result in his suspension from the Police Department.
The assault followed a prolonged highway confrontation between the S.U.V. and group of motorcyclists on a sunny Sunday afternoon. Four other motorcyclists have been charged so far; the police were actively searching for others, releasing images taken from video of four men on Tuesday.
