Yesterday, it was reported that an off-duty undercover NYPD officer participated in last Sunday's violent group motorcycle ride, and did not intervene when fellow bikers brutally beat the SUV driver who collided with some of the motorcyclists. Today, it's been reported that up to half a dozen undercover and off-duty NYPD officers either were on the highway when driver Alexian Lien was confronted by the motorcyclists, or witnessed the assault at West 178th Street.

According to DNAInfo, internal affairs has the names of two detectives, one sergeant and three police officers who were involved in the incident. Sources tell ABC that at least two detectives were undercover with the biker group, and witnessed the attack on Lien and did not directly intervene. At least one of them is a narcotics officer who is reportedly a motorcycle enthusiast who belongs to the group First Line Soldiers, which is based in New Rochelle.

“It does not appear that he got involved at the scene,” a law-enforcement source told the Post about the unnamed narcotics officer, who has now hired a lawyer. The source said the cop was not investigating the group of motorcyclists, but “he didn’t want to blow his cover."

According to the News, that officer told colleagues he didn't intervene because he feared losing his job like Detective Gescard Isnora, an undercover cop who was involved in the Sean Bell shooting in 2006, and ultimately was fired and lost his pension and health benefits for shooting his weapon while undercover.

None of the officers came forward until late Wednesday, four days after the incident. All the officers likely will face disciplinary measures because they did not immediately come forward and tell their supervisors they were there.