The undercover NYPD detective accused of shirking his police duties and joining a mass of angry motorcyclists who attacked an SUV driver on the West Side Highway more than two years ago has been cleared of the top charges against him, gang and first-degree assault, but convicted of lesser assault charges.

A judge delivered the verdict Tuesday in the bench trial of detective Wojciech Braszczok, finding him not guilty of gang assault, attempted gang assault and first-degree assault, but guilty of second- and third-degree assault, coercion, riot and criminal mischief in the September 2013 attack on SUV driver Alexian Lien.

Braszczok's co-defendant, Robert Sims, was also convicted of the lower counts but acquitted of the top charges in the motorcycle rally that devolved into pandemonium and became a highway horror story to millions who saw a helmet-camera video posted online.

Last week, Braszczok testified in his own defense, saying he didn't intervene in the melee because he feared for his safety and didn't admit his involvement in it because he worried he'd get fired.

Braszczok was off duty at the time and never carries a gun or badge identifying himself as an officer because it could compromise his undercover work, he said. The first time he noticed Lien was when the driver stopped the highway amid a bunch of bikers and then seemed to accelerate suddenly, striking a biker and speeding off.

"I thought he was the aggressor, he took off, he fled the scene," he said in explaining why he followed the driver north on the highway.

Prosecutors suggested Braszczok and the other bikers had made the West Side Highway a personal playground, popping wheelies, slapping car hoods and terrorizing Lien and his wife and toddler, who were headed to New Jersey to shop. Lien says he feared for his life so he drove away, running over a biker. Prosecutors say Braszczok barreled after Lien and was among the bikers who forced the Range Rover to a stop on a side street. The detective eventually drove away while Lien was pulled from the car and attacked on the street.

But Braszczok said last week he followed Lien because he wanted to "stop the car from running more people over." When he got off his bike, he intended to tell Lien to stop driving, but he heard a bang and saw the SUV window break, and then started to fear for his safety, so he left.

"I should have called 911, but I didn't," he said. He said he regretted the decision, adding he believed the police were on their way.

Braszczok also said he wasn't truthful with his superiors about the altercation because he worried he'd be fired or reprimanded — but not because he'd thought he had committed a crime.

The defendants opted to have a judge, not a jury, determine the outcome. Eleven men were indicted in the melee; the others have pleaded guilty to charges including assault and riot and face sentences of probation to two years in prison.

Lien was not charged. The biker Lien hit, Edwin Mieses, was paralyzed.

Braszczok, who has worn a black sack on his head outside court to protect his undercover identity and showed his face for the first time outside the building Tuesday, did not comment on the verdict.

His attorney said his client had been vindicated.

Luther Williams, an attorney for co-defendant Sims, said both his client and Braszczok received a fair trial, though he was disappointed about the convictions on the lower counts.

"This was bad behavior from many folks," Williams said.

It wasn't immediately clear how much prison time the men might face.