Undercover NYPD Cop Watched SUV Driver Get Beaten

Oct. 4, 2013— -- The man who police say was seen on video using his helmet to smash the driver's side window of an SUV besieged by motorcyclists in New York City surrendered to police late Friday.

Reginald Chance, 38 of Brooklyn, N.Y., allegedly was the man shown hitting the Range Rover with his helmet before the video cut off and the driver, Alexian Lien, allegedly was assaulted.

Chance's possible role in the alleged assault beyond the window smashing was not immediately clear.

There was no immediate information on charges or an arraignment.

In addition, the NYPD was investigating whether there may have been as many as five off-duty police officers in the sport bike ride that ended with the alleged assault on Lien.

At least one off-duty undercover New York City police officer was among the crowd of motorcyclists on the scene as Lien was beaten on Sunday, officials confirmed to ABC News Friday.

The undercover narcotics cop did not intervene in the beating out of fear that his cover would be blown, sources said.

The cop's identity has not been released by the NYPD. According to officials, the officer notified his superiors days after the incident. He was a motorcyclist who was there on his own time, they said.

The information was part of the ongoing investigation by the NYPD and the Manhattan district attorney into the confrontation and beating that happened Sunday afternoon between a group of 20 to 30 motorcyclists and Lien, caught on video and uploaded to the Internet.

The officer's involvement was also the subject of an Internal Affairs investigation, sources said.

Police were looking into accusations from other riders that there were more officers present.

Robert Sims, 35, who allegedly grabbed the SUV's door about five minutes into the video, also was in custody after he turned himself in to police in Brooklyn earlier Friday, NYPD officials said. Charges against him were pending. Sims was arrested in 1998 for possession of a loaded firearm and a samurai sword, and he served eight months in jail, police said.

Lien was driving his SUV on the West Side Highway in Manhattan with his wife and 2-year-old as part of a wedding anniversary celebration around 2 p.m. Sunday when their SUV was surrounded by the motorcyclists, who were doing an annual ride through the city, police and Lien's wife said.

The bikers tried to slow traffic and one biker cut Lien off, slowing down and leading Lien to bump into the biker, police said. The group of motorcyclists then slowed down further and surrounded the SUV, causing Lien to accelerate away from the group. Lien's wife, Rosalyn Ng, said that her husband feared for their lives when he decided to take off to get away from the group. As he sped off, Lien hit some of the motorcyclists, critically injuring one, authorities said.

Other motorcyclists then chased Lien's SUV and then bashed in his windows, pulled him out of the car, and beat him, police said.

The undercover police officer was at the scene where Lien was beaten, officials said.

A source briefed on the case told ABC News that in the days since the attack "new evidence has been coming in and it will give prosecutors much better evidence for charging the attackers."

The new evidence included additional video footage and stills compiled from a variety of cameras that were situated around the scenes of the chase and melee, the source said.

ABC News' Mark Crudele contributed to this report.