COBLESKILL, N.Y. (AP) - A limousine service operator was charged Wednesday with criminally negligent homicide in a crash that killed 20 people, while police continued investigating what caused the wreck and whether anyone else will face charges.

Nauman Hussain, 28, showed little emotion as he was arraigned Wednesday evening in an Albany-area court, and he ignored shouted questions from reporters as he left after posting $150,000 bond. A judge had entered a not guilty plea for him.

Earlier, his lawyer said that Hussain wasn't guilty and that police were rushing to judgment in investigating Saturday's stretch limo wreck.

But State Police Superintendent George Beach said Hussain hired a driver who shouldn't have been behind the wheel of such a car, and the vehicle shouldn't have been driven after state inspectors deemed it "unserviceable" last month.

"The sole responsibility for that motor vehicle being on the road on Saturday rests with Nauman Hussain," Beach said, though he noted that investigators continue looking into whether anyone else should be held accountable in the crash.

Hussain's car was packed with luggage when he was stopped Wednesday on a highway near Albany, Schoharie County District Attorney Susan Mallery said.

Hussain's lawyer, Lee Kindlon, said his client felt unsafe at home because he'd gotten threats.

The company, Prestige Limousine, has come under intense scrutiny since a 19-seater limo ran a stop sign and plowed into a parked SUV at the bottom of a long hill Saturday. The impact killed two pedestrians and 18 people in the limo, which was taking a group to a birthday bash.

Kindlon said his client handled only marketing duties and phone calls, while his father ran the company, though police called Hussain its operator.

"My client is not guilty," Kindlon said. "The police jumped the gun in charging him with any crime."

Under New York law, criminally negligent homicide involves not perceiving a substantial, unjustifiable risk that leads to someone's death. It's punishable by up to four years in prison.

Charged with a single count involving all 20 victims, Hussain spoke in a clear, firm voice as he gave brief answers to the judge's questions about his finances and living arrangements. He turned twice to nod at relatives in the courtroom audience.

Hussain has had a brush with authorities before. State police accused him and his brother of claiming each other's names after a 2014 traffic stop, which happened while the brother was driving without a valid license.

Their father, Prestige Limousine owner Shahed Hussain, also has a history with law enforcement - as a government informant in terror plot investigations after the Sept. 11 attacks.

Saturday's crash appeared to be the nation's deadliest traffic accident since a bus full of Texas nursing home patients caught fire while fleeing 2005's Hurricane Rita, killing 23.

Gov. Andrew Cuomo said Monday that the limo driver didn't have the required commercial license, and that Prestige Limousine "had no business putting a failed vehicle on the road."

The limo had been written up Sept. 4 for code violations, including a problem with the antilock brakes' malfunction indicator system.

A sticker was placed on the vehicle declaring it "unserviceable," state Department of Transportation spokesman Joseph Morrissey said.

It was the latest in a series of inspection knocks for the Gansevoort, New York-based company. Four of its limos were cited this year with a total of 22 maintenance violations, though none was deemed critical.

Kindlon told CBS News on Tuesday the "safety issues had been addressed and corrected," saying many were minor. But Morrissey said any assertion that the limo involved in the crash had been cleared for service was "categorically false."

Kindlon said he didn't think the infractions contributed to the crash. He suggested the driver, who died in the crash, might have misjudged his momentum on the hill.

The T-intersection at the bottom was a known danger spot, Kindlon noted. It was rebuilt after a deadly 2008 wreck, but there have since been other accidents at the junction.

"I think, frankly, the Department of Transportation and the state of New York is doing a great job in saying, 'Look over there! It's not our fault!'" Kindlon said.

The limo's driver, Scott Lisinicchia, had been told he didn't have the proper license to drive it during an Aug. 25 traffic stop, state police said Wednesday. They said a trooper issued violations, advised that Lisinicchia couldn't drive the limo and "took steps to ensure that the vehicle was taken off the road."

The Times Union of Albany first reported about the traffic stop.

Lisinicchia's family, meanwhile, said he was unwittingly put in an unsafe vehicle.

Kim Lisinicchia told CBS in an interview broadcast Wednesday that her husband repeatedly said he wouldn't drive the car the way it was. But then "he trusted in what the limo company said, that the cars were all right," she said.

She said her husband was an excellent, veteran driver with over 20 years of experience in tractor-trailers and was in fine health.

"I feel for these victims," the widow said. "I am in no way trying to make it seem like it's about me or my husband. I just want my husband to be vindicated. I have to stand for him, 'cause nobody else will."