Nine motorcyclists, including an off-duty undercover NYPD officer, have been arrested for their involvement in the road rage incident that ended in the vicious beating of driver Alexander Lien. Now the Post reports that police are looking to arrest four more people connected to the incident.

The Post's police sources tell the tabloid that the department is "pulling out all the stops" to identify the makes and models of the suspects' motorcycles. Three of the machines have around 300 registered owners apiece. “They are in the beginning stages of going to every address to see what they can learn,” a source says.

One of the nine suspects who were arrested, 37-year-old Reginald Chance, was described by the Manhattan DA's office as the biker who "set into motion a chain of events that resulted in the driver being dragged out of his vehicle and beaten." Chance has 21 prior arrests from charges ranging from robbery to narcotics and gun possession.

Though several off-duty NYPD officers participated in the group ride, the only one who has been charged is 32-year-old Detective Wojciech Braszczok, who was assigned to infiltrate Occupy Wall Street.

Lien, who was beaten in full view of his wife and child, suffered two black eyes, multiple cuts that required stitches, and injuries to his back, hands, and right shoulder.

Edwin Mieses, Jr., the biker who Lien ran over as he attempted to escape the pack of motorcyclists, may never walk again.