An undercover NYPD officer involved in the motorcycle assault case has been arrested.

The undercover officer is said to be 29 years old.

Sources now say another video obtained by Internal Affairs contradicts the original story of the off-duty undercover detective, who admitted being in the group of bikers on the West Side highway, but claimed he only saw the tail end of the attack uptown. The detective claimed he drove away without taking any action to avoid blowing his cover, but we’ve been told he can be seen punching the rear window of the SUV, which later shattered, throwing a kick at the passenger door, and then speeding off on his bike. The Police Commissioner today, not saying much.

“We have put a police officer on modified assignment and the investigation is going forward. We anticipate identifying more people,” NYPD Commissioner Raymond Kelly said.

Sources say a second detective is also believed to have been among the riders, but not present for the attack. That detective is already on modified duty after being arrested in August during a domestic dispute at an intersection in Queens. The criminal complaint says the cop went after a responding officer: “He shoved him in his chest several times in a forceful manner.” The charges will be dismissed if the detective stays out of trouble for six months.

“We are looking at all aspects of this investigation,” Kelly said.

Another video that’s emerged in the case shows SUV driver Alexian Lien on the ground in Washington Heights, surrounded by a mob. CLICK HERE to see the full video on YouTube.

In addition, police released the photos of 4 more suspects wanted for questioning in the assault. VIEW THOSE PHOTOS

A grand jury hearing is evidence against in the assault cases already filed. That will include the victim making a statement for prosecutors.

Meantime, a fourth suspect has been arraigned on multiple charges related to the incident.

On Tuesday, 29-year-old Craig Wright became the fourth motorcyclist arraigned in connection with this incident. He pleaded not guilty to charges of assault, gang assault and unlawful imprisonment and was ordered held on $100,000 cash bail/$150,000 bond.

Prosecutors alleged that Wright punched Lien through the window of the SUV and then kicked him while he was on the ground.

He is due back in court on October 11.

Sources say police tracked down Wright by the license plate on the motorcycle, which belonged to his uncle.

(Source: WABC)