Update 6:34 p.m. The undercover NYPD cop riding with the motorcycle gang has been arrested and charged with criminal mischief for his role in the attack on the SUV.

An off-duty undercover NYPD narcotics cop who rode with the motorcycle biker gang that viciously beat SUV driver Alexian Lien actually participated in the road-rage attack, according to the New York Post.

The unidentified cop, a seven-year NYPD veteran, allegedly smashed in the back window of the Range Rover while other bikers pulled Lien from the vehicle. The cop had initially told investigators that he rode up to the scene just as the beating was ending, and he didn’t want to blow his cover.

The police officer turned in his gun and badge and has been placed on desk duty while the NYPD's Internal Affairs unit investigates the matter, the Post reported. He didn’t come forward about his involvement until more than three days after the New York City road rage incident.

According to CNN, there is video footage that shows the cop’s involvement in the attack, but the NYPD is holding onto it for now.

“The cop is a total mope. F*****g embarrassment, ’’ one source told the Post. “They should can him immediately. Anyone else who was even peripherally involved should be canned.”

DNAinfo notes that there were six off-duty undercover NYPD cops who rode with the motorcycle gang that day.

However, that might be about to change, according to a separate report in the Post. The NYPD is looking into arresting the cop tonight and charging him with felony criminal mischief. He could be face four to seven years in prison if convicted.

According to the Post, the Internal Affairs unit wanted to charge the police officer with gang assault, but it would have had to show that he intended to cause serious physical injury, something that can’t be proven.

So far, four motorcyclists have been arrested in relation to the SUV road-rage incident. Reginald Chance, 37, and Robert Sims, 35, have been charged with gang assault. Another biker, Craig Wright, 29, has also been arrested and charged with gang assault after having punched Lien through the broken driver’s side window.

Christopher Cruz, 29, has been charged with reckless endangermen; he could be seen applying his brakes directly in front of Lien’s SUV during the video that went viral last week. In an interview with ABC News, Cruz said he doesn’t feel responsible for igniting the violent incident.

“I was looking over my shoulder to see where my friends were,” he told ABC News. “I wanted them to pull in front so I could follow them. I didn’t brake, but when I looked over my shoulder, my hand came off the throttle a little, but the driver didn’t slow down at all and bumped me.”