The horrific limousine crash that killed 18 people celebrating a birthday and two pedestrians over the weekend in upstate New York renewed questions over the safety and regulation of the stretch vehicles.

The 2001 Ford Excursion limousine involved in the deadly crash was "a chopped vehicle," New York Gov. Andrew Cuomo said Monday, meaning it had been cut from a passenger vehicle and extended.

The limousine also did not have a certification that it had been extended "in a way that was compliant with federal law," Cuomo said.

Experts said such modified vehicles face less regulations than typical passenger cars and often have had features removed intended to keep occupants safe.

"Before they're modified, they do have to meet different safety regulations in the U.S., but once a vehicle is modified there are many exemptions," said Raul Arbelaez, an engineer with the Insurance Institute for Highway Safety. "They don't have to go back and prove that they meet any of the crash safety criteria."

Arbelaez said the sheer weight of the vehicle, likely around 10,000 pounds after it was modified, and its 18 occupants going at highway speeds would contribute to the severity of a crash.

"That is a lot to ask of the same four tires and brakes that vehicle came with" originally, he added.

Television networks broadcast at the scene of a fatal limousine crash in Schoharie, New York, on Oct. 8. Hans Pennink / AP

Arbelaez said that while he could not say this was the case for sure, "it doesn't seem likely" the stretch limousine would have had enough seat belts for all 18 people in the car.

Even if the vehicle did have enough, research has shown many people don't wear seat belts in stretch limousines, Arbelaez said.

From 2012 to 2016 there were 19 deaths involving limousines, he said. Twelve of those deaths were passengers in a limousine and of those, all but one were not wearing their seat belts.

National Transportation Safety Board Chairman Robert Sumwalt said at a news conference Monday afternoon that officials were working to determine if the vehicle was converted into a limousine in accordance with federal regulations and if its seat configuration, two in the front and 17 in the back, "may have contributed to the injuries."

Investigators have seized three other vehicles from the company in addition to the one involved in the crash, New York State Police Major Robert Patnaude said at that news conference.

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

Patnaude said police had located the owner of the limousine company and that he was currently in Pakistan.

Prestige Limousine of Gansevort, New York, is owned by Shahed Hussain and is operated by Hussain’s son, according to the company's attorney.

Adding a bizarre twist to the tragic plot, the owner of the company is a former FBI informant in several terrorism cases, according to multiple federal law enforcement officials, public records, and an attorney for the limo company.

Cuomo said earlier Monday that the limousine involved in the fatal crash had failed an inspection last month and should not have been on the road. The driver of the vehicle, Scott Lisnicchia, 53, also did not have the specific commercial driver's license required to drive that limousine.

Arbelaez said such limousines are "massive vehicles that need to be operated in a very specific way" by a person who has been specially trained and licensed. He added that while limousines can be safe and limousine deaths make up a small part of driving deaths overall, consumers should work to ensure they are dealing with reputable companies with trained and licensed drivers.

Deborah Hersman, president and CEO of the National Safety Council, said many consumers may not realize that some stretch limousines don't "have many of the safety features that your own car does."

Hersman — a former chairwoman of the National Transportation Safety Board under President Barack Obama — also stressed that a major issue was the lack of oversight once a car is modified and stretched.

"Once they're changed they may not have to be re-inspected, they don't have to be crash-tested and they may not have to have emergency exits, or fire extinguishers, depending on how large the vehicle is. They may be introducing new risks," she said.

She added that the U.S. currently has "a patchwork system when it comes to oversight of these vehicles."

"It's really important to re-evaluate where we are and to recognize that this Frankenstein system that we have across the country isn't serving consumers well," she said.

Saturday's crash was reminiscent of limousine accidents in recent years where a celebration ended in tragedy. In 2005, a limo driver and a 7-year-old girl were killed after an intoxicated driver crashed into them after a wedding on Long Island. The driver in the other car was convicted of murder.

In 2013, five women celebrating a bridal shower died when a limousine burst into flames on California's San Mateo bridge in San Francisco.

And in 2015, four women on a winery tour in Suffolk County, N.Y., were killed after they were struck by a pickup truck as their limousine was trying to make a U-turn.

A New York grand jury in that case found that stretch limousines don't often have security measures including side impact airbags, rollover protection bars and accessible emergency exits. That grand jury called on Cuomo to assemble a task force on limousine safety.

Cuomo's office and the New York Department of Transportation did not immediately respond to NBC News' request for comment on any changes that had been made following the grand jury report.

But Cuomo told reporters earlier Monday at a Columbus Day parade that "the federal government has the primary set of regulations for limousines."

"Sometimes the issue is the law worked fine, and the regulation worked fine. They were just broken," he said.

"The owner of the company had no business putting a failed vehicle on the road," he said.

The company, Prestige Limousine, said in a statement Monday afternoon that 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 statement said.

Earlier, a company spokesperson told NBC's "Today" that they are "devastated by this loss," but declined to comment further because their owner was out of the country.