The New York Police Department has opened an internal probe of an undercover officer and several off-duty officers who were present when motorcycle club members beat up an SUV driver.

An undercover officer didn't intervene when bikers attacked Alexian Lien on Sept. 29 after a road-rage confrontation because he didn't want his cover blown, reports ABC News. There may have also been several off-duty officers present.

The incident began as the motorcycle club riding together surrounded the black SUV driven by Lien in upper Manhattan. After striking one of the bikers on West Side Highway, Lien stopped his vehicle and was surrounded. He accelerated, running over biker Edwin Mieses.

After a wild pursuit, Lien stopped in New York City traffic, allowing the bikers to jump off their motorcycles. Reginald (Reggie) Chance, 37, then allegedly smashed Lien's window with his helmet. Other bikers then pulled Lien from the vehicle and began beating him as his wife and child sat in the vehicle. The mob backed off when several bystanders intervened.

Chance, who is facing assault and gang assault charges, flipped off reporters at a court hearing on Sunday, reports the New York Daily News. Video footage of the confrontation was captured by one of the riders on a helmet cam.