While two men involved in an alleged attack on a SUV driver in New York City are in custody, police say they are scouring hours of footage and photos taken at the scene to pursue others who may have played a role in the beating.
The NYPD is 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 Range Rover driver Alexian Lien.
Overnight, the NYPD released photos of what police said is a person of interest who is believed to have been involved at the scene of the alleged assault.
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 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 chased Lien's SUV and then bashed in his windows, pulled him out of the car, and beat him, police said.
Two men seen on video committing the most violent actions at the scene are in custody.
Robert Sims, 35, who allegedly grabbed the SUV's door about five minutes into the video, turned himself in to police in Brooklyn earlier Friday, NYPD officials said.
He faces charges of gang assault, assault and criminal possession of a weapon, police said this morning.
Sims was arrested in 1998 for possession of a loaded firearm and a samurai sword, and he served eight months in jail, police said.
Reginald Chance, 38, Brooklyn, N.Y., also surrendered to police late Friday. He allegedly was the man seen on video using his helmet to smash the driver's side window of the Range Rover before the video cut off and the alleged assault took place.
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.
An undercover 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. The incident was caught on video and uploaded to the Internet.
The officer's involvement was also the subject of an Internal Affairs investigation, sources 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, Colleen Curry and Alexis Shaw contributed to this report.