An off-duty undercover New York Police Department detective has turned himself in to face charges after video showed him pounding on the SUV at the center of a bloody road rage incident between the SUV driver and a band of motorcyclists on New York City’s Westside Highway.

The detective initially told his superiors he was not involved in the Sept. 29 attack on the SUV driver, who was pulled from his car and stomped on in front of his terrified wife and child, and said he did not intervene for fear of blowing his cover.

But the detective, identified by The New York Times as Wojciech Braszczok, was seen in a video pounding on the SUV’s rear window and kicking its side before leaving the scene on his motorcycle, according to multiple reports.

The New York Daily News, citing a police source, said the detective surrendered with his lawyer on Tuesday and was taken to Manhattan Central Booking shortly after the Manhattan district attorney approved his arrest.

According to the Times, Mr. Braszczok faces charges of riot and criminal mischief and will be suspended after his arrest.

On Monday, Braszczok’s lawyer, Philip Karasyk, said his client had observed, but did not directly participate in, the altercation.

The detective did not have a badge, or gun, and was aware of cases in which officers had been suspended or dismissed for blowing their cover, "he had no other option, so he drove away," Mr. Karasyk, who works with the Detectives’ Endowment Association, told the AP.

While undercover status can excuse officers from directly intervening when they observe a crime, or immediately reporting the crime to the police, being undercover doesn't offer officers blanket immunity, says Eugene O'Donnell, a former NYPD officer and current lecturer at the John Jay College of Criminal Justice in New York City.

"Violence is usually the bright line," Mr. O'Donnell says. "Watching somebody get hurt is one thing, hurting someone would be another thing," though every case is nuanced, he adds.

The NYPD internal affairs investigators had been looking into the undercover detective's conduct because he did not report the incident until three days after the altercation.

However, the police officer's delay in coming forward wasn’t unusual, says O'Donnell. An undercover officer can't just traipse into the local precinct office and report a crime, O'Donnell explains. This could blow the officer's cover entirely, or put the secrecy of a larger investigation at risk.

There isn't a hard and fast rule on the time frame, says O'Donnell, but the officer is obliged to take appropriate steps to report his observations when it becomes possible.

The road rage incident occurred when a band of motorcyclists swarmed Alexian Lien’s black Range Rover in Washington Heights, after Mr. Lien bumped into one of the motorcyclists, later identified as Christopher Cruz.

Riders then dismounted their bikes, approached the SUV, and began hitting the vehicle. Lien then took off, and collided with motorcyclist Edwin “Jay” Mieses Jr.

Lien’s wife, who was in the car with her husband and their 2-year-old daughter, said her husband took off in fear.

The group of bikers then swarmed Lien's car, causing him to stop the vehicle, at which point bikers began hitting Lien's SUV and breaking the car's windows before prying Lien from inside and beating him up.

Mr. Mieses is in the hospital with two broken legs and a spinal injury. Lien received stitches.

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Before Braszczok turned himself in, four motorcyclists have been charged in the incident. Lien has not been charged with hitting Mieses.

The YouTube video that recorded part of the incident has been replayed more than 7 million times and has helped police to identify suspects in the case.