The article indicates he was off-duty so he wasn't infiltrating the gang as part of an undercover operation. He was just one of them...
http://www.cnn.com/2013/10/04/us/bikers-attack-video/index.html?hpt=hp_c2
http://www.cnn.com/2013/10/04/us/bikers-attack-video/index.html?hpt=hp_c2
New York (CNN) -- A New York police officer saw much of a confrontation between fellow motorcyclists and a Range Rover driver -- which ended with five injured, including the SUV driver -- but didn't step in, a law enforcement source said.
The police officer, who works undercover, was off-duty and riding with the motorcycle club he belongs to when the incident occurred Sunday. But he didn't tell his superiors about what happened until Wednesday, the source said.
It's not clear why the officer waited so long to report what he saw. The officer, who has hired a lawyer, is being investigated by the New York Police Department's internal affairs unit. But he may not have been legally obligated to immediately intervene, according to the same source.
Asked about this officer, Deputy Police Commissioner John McCarthy declined comment, saying only, "The investigation is ongoing."