The undercover NYPD narcotics officer involved in last week's violent SUV attack was one of several bikers caught on video punching and pounding the outside of Alexian Lien's Range Rover, according to a report in the New York Post.

The officer, a seven-year-veteran of the NYPD, initially told investigators he didn't intervene because he arrived after the beating was almost over, but the Post's “disgusted” sources said an unreleased video showed otherwise.

The NYPD's Internal Affairs unit hopes the officer will be held responsible for the attack, though last week's decision by the District Attorney to drop charges against Allen Edwards, who was also seen punching Lien's window, might prevent formal charges from being filed. However, the officer will likely face internal discipline; he's already been placed on modified duty, which required him to turn in his gun and badge.

The officer is reportedly one of six NYPD cops who were riding with the motorcycle group during or before the attack; two detectives, one sergeant, and three police officers are being investigated, according to DNA Info. None of the police officers intervened in the beating.

Meanwhile, a fourth suspect was arrested and charged on Monday. Chris Wright, 29, was arrested after police identified him as one of the bikers attacking Lien in an unreleased witness video. The video reportedly shows Wright punching through the shattered driver's-side SUV window and, later, kicking Lien while he's on the ground. Wright was charged with gang assault and assault.

Police are searching for at least two more suspects.