The indictment filed Friday says undercover detective Wojciech Braszczok was charged with gang assault, criminal mischief, riot and other counts.
Prosecutors say the 10-year-veteran of the NYPD participated in the Sept. 29 attack.
Braszczok was initially under investigation because he did not immediately report that he witnessed the beating of Alexian Lien. But prosecutors say they have video of Braszczok actively participating in the confrontation.
Investigators say Braszczok is seen on video punching the rear window of the SUV, while his attorney says video shows the detective at least 12 feet away when Lien was attacked.
Video of the attack recorded by one of the bikers in the group shows the motorcyclists slowing their speed as they surround the SUV driven by Lien, and the SUV then bumping the fender of a motorcyclist in the group.
Twenty to thirty bikers then surrounded the SUV and began damaging the vehicle, causing Lien to take off and exit the highway as his tire deflated.
In his attempt to flee, Lien hit a motorcyclist before speeding off, causing the entire group of bikers to take off after him. That's when the bikers then assaulted Lien in front of his wife and 2-year-old child.
He has not been charged in connection with his role in the incident.
ABC News and The Associated Press contributed to this report.
