The limo that crashed and killed 20 people failed inspection. And the driver wasn't properly licensed.

Schoharie, New York (CNN) The modified limo that crashed and killed 20 people wasn't even supposed to be on the road, New York's governor said Monday.

On top of that, the driver "did not have the appropriate driver's license to be operating that vehicle," Gov. Andrew Cuomo said.

The startling revelations bring more anguish to those grieving the deaths of 20 people in the quaint town of Schoharie.

Before the disaster, the limo was full of exuberance -- 17 birthday party guests who had many reasons to celebrate. There were newlyweds and young couples and four sisters, all on their way to revel at an upstate New York brewery.

But for reasons still unknown, the limo plowed through a stop sign, crashed into a parked SUV and caused the deadliest US transportation accident in almost a decade.

All 17 passengers were killed. So was the limo's driver. So were two pedestrians.

As more details emerge about the apparent broken rules, investigators also are wondering whether the unusual structure of the limo may have contributed to this mass tragedy.

The birthday party guests were riding in a 2001 Ford Expedition that had been converted into a limousine.

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"That vehicle was inspected by the New York State Department of Transportation last month and failed inspection and was not supposed to be on the road," Cuomo said.

"The driver needed what what's called a CDL, a commercial driver license with a passenger endorsement. The driver did not have that proper license," Cuomo added.

The limo company has been identified as Prestige Limousine Chauffeur Service in Gansevoort, New York, according to an official with knowledge of the investigation.

US Department of Transportation records show Prestige Limousine Chauffeur Service has two drivers and three vehicles. Its vehicles were inspected five times in the last two years, and the company has had four vehicles taken out of service.

In a statement Monday, the limo company said it "extends its deepest condolences to the family members and friends of those who tragically lost their lives on Saturday. We are performing a detailed internal investigation to determine the cause of the accident and the steps we can take in order to prevent future accidents."

The company said it has "voluntarily taken our fleet of vehicles off of the road during the investigation." The company has already met with federal and state investigators and plans to do so again, the statement said.

Cuomo said officials are working on "a cease-and-desist order to stop Prestige Limousine from operating until the investigation is concluded."

State Police investigators have recovered the vehicle's airbag control module, which is the equivalent of the vehicle's black box, Maj. Robert Patnaude said.

"That company and that vehicle have been under scrutiny of [Department of Transportation] in the past," he said, declining to elaborate.

State police officials seized three of the company's vehicles, in addition to the modified limo involved in the crash, Patnaude said.

National Transportation Safety Board chairm Robert Sumalt said the limo was configured for 19 seats. Some seats had lap-shoulder belts, but it wasn't immediately clear if all the seats were equipped with seat belts and whether anyone had them on, Sumwalt said.

In limos in New York, rear passengers are not required to wear seatbelts, according by Sumwalt.

He said some seats remained anchored to the floor during the crash. Sumwalt said there was extensive damage to the front of the limo, mostly on the driver's side. The limo's engine compartment has been pushed back in to the front of the passenger compartment, indicating a "high energy impact," Sumwalt said.

No skid marks were observed but the damp road conditions could have mitigated any skid marks, he said.

The federal agency doesn't' know the limo's speed at this point at the time of the crash, Sumwalt said.

The NTSB will look at a number of factors, including the driver's fitness, whether fatigue was an issue, the company's compliance with state and federal regulations and its record of prior crashes, Sumwalt said.

Those in the limo weren't just friends -- many were family.

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Four sisters -- Mary Dyson, Abby Jackson, Allison King and Amy Steenburg -- all perished in the crash, state Assemblyman Angelo Santabarbara said. Steenburg's husband Axel Steenburg also was killed.

Many of the victims were from the upstate city of Amsterdam, about 20 miles north of the crash site. Jackson was a special education teacher in Amsterdam, said Santabarbara, who represents the part of New York where the crash happened.

Valerie Abeling said her niece, Erin Vertucci McGowan and Erin's husband Shane McGowan, died together. They got married just four months ago.

"It's a horrible tragedy, and there's no words to describe how we feel," Abeling said.

"These were young couples, just got married and had their whole lives ahead of them."

Erin Vertucci and Shane McGowan were married in June.

Karina Halse said she's struggling with the loss of her sister, Amanda Halse, who was killed along with her boyfriend.

"My heart is completely sunken," Karina said. "I can't even imagine how it happened, or why it happened."

Amanda Halse, 26, was the "peacekeeper of the family," her sister Karina said.

And Barbara Douglas isn't just grieving the deaths of her two nieces. She's mourning the loss of two mothers.

"They were fun-loving. They were wonderful girls," Douglas said. "They'd do anything for you, and they were very close to each other."

Douglas' face grew increasingly somber as she thought of her nieces' three children.

"They now have no parents," Douglas said.

Questions abound over the structure of the limo

Federal, state and local investigators flooded the tiny town of Schoharie to try to understand what happened

"We don't know the cause of the accident, if it was a vehicle malfunction, if it was a driver malfunction (or) a driver error," Cuomo said.

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The crash happened outside an Apple Barrel Country Store & Cafe. Resident Bridey Finnagen said it was loud enough to hear from down the road.

"I heard a loud bang. I came out my front door to see what was going on," Finnagen told CNN affiliate WTEN

"I saw a lot of people here at the Apple Barrel out in the parking lot. Then I heard screaming. Then I saw this large van, a very unusual looking vehicle, out here in Schoharie in the bushes and really wrecked, hit a tree."

These kinds of altered vehicles have worried officials, said Peter Goelz, former managing director of the NTSB. That's because after-market modifications often affect a vehicle's structural integrity and safety.

It's not clear whether the driver was speeding or whether the brakes were working said Chris Fiore of the New York State Police. In limousines, rear passengers are not required to wear seat belts, Goelz said.

The crash was so catastrophic, it stunned even veteran safety experts.

"Twenty fatalities, it's just horrific," Sumwalt told reporters Sunday.

"I've been on the board for 12 years and this is one of the biggest losses of life ... This is the most deadly transportation accident in this country since February of 2009."