NEW YORK (CBSNewYork) — An off-duty undercover New York City police detective accused of taking part in a gang assault on an SUV driver was cross-examined in court Thursday.

As CBS2’s Alice Gainer reported, the prosecutor asked Wojciech Braszczok about initially telling his NYPD handler that he didn’t see the September 2013 attack.

“So you lied to him?” the prosecutor said.

“Yes, I lied to him,” Braszczok said.

“The reason you lied (was) you were concerned about departmental problems you might get into if you told the truth?” the prosecutor asked.

“Yes,” Braszczok answered.

Braszczok is the biker seen on video shattering the rear window of an SUV with his helmet.

The 44-year-old cop maintains he attacked the car out of fear.

Inside the SUV was a frightened family — driver Alexian Lien, his wife and young daughter — who’d been stopped several minutes before on the West Side Highway by bikers allegedly trying to claim the highway for their illegal road rally.

Braszczok said he first saw the Range Rover when it was already surrounded by bikers.

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Lien took off, driving over and severely injuring a biker in the process.

Braszczok said he chased down the SUV, along with the others, thinking the people inside were the aggressors.

Lien was later pulled from the vehicle, beaten and stomped. Braszczok said he failed to help the driver because he felt unsafe and threatened by whomever else was in the vehicle, WCBS 880’s Irene Cornell reported. He said he didn’t know that the only other people in the SUV were Lien’s wife and child.

The detective said he did not have his gun or badge on him that day while he was off-duty and did not identify himself as an officer during the attack.

Braszczok admitted participating in the rally as a member of a police-affiliated club called Front Line Soldiers.

In court, he was asked about group text messages with other members after the attack.

Braszczok texted, “The media has to blame someone so no one — we don’t speak about bike club.”

The prosecutor asked him: “A reference to the Brad Pitt movie ‘Fight Club,’ you were telling them not to talk about what happened?”

“Yeah, not to talk about it, the club, because we were getting blamed, because we were getting blamed online,” the cop answered.

Braszczok and a co-defendant, Robert Sims, who has yet to take the stand, are charged with assault.

Closing arguments are expected to begin Friday.

The judge said the deadline for him to reach a verdict in the bench trial is Tuesday.