By John Miller, Elizabeth Wolfe and Celina Tebor, CNN

(CNN) — Investigators believe a New York man and his wife were the two people killed in a car that crashed and exploded at a US-Canada border crossing near Niagara Falls on Wednesday, law enforcement sources say, and the FBI sees no link to terrorism.

Alarms were raised from New York to Washington, DC, late Wednesday morning after the incident on the US side of the Rainbow Bridge crossing. Investigators believe the couple was traveling in a Bentley at high speed when it struck a curb at the checkpoint, then hit a guardrail that sent the vehicle airborne and into a screening area before it exploded, according to the sources.

Despite initial concerns of a terror attack, the FBI has not found any connection to terrorism and no explosives were found at the scene, the agency’s Buffalo field office announced Wednesday night. The case is being turned over to local police as a traffic investigation.

“I want to be very, very clear to Americans and New Yorkers: At this time there is no indication of a terrorist attack,” New York Gov. Kathy Hochul said at a news conference Wednesday evening.

“Two individuals died in the vehicle,” Hochul said, noting the car is associated with a western New York resident.

Investigators believe the man who diedhad plans to attend a KISS concert in Canada, but when it was canceled he went to a casino in the US instead. The crash occurred sometime after the couple left the casino, the sources said.

“There’s a lot of unanswered questions,” Hochul said of the vehicle’s occupants Wednesday. She noted it was still unclear whether the crash was an accident or an intentional act.

The explosion prompted a temporary shutdown of all four bridges between Canada and the US near Niagara Falls on one of the busiest travel days of the year. Three of the bridges reopened later Wednesday, but Rainbow Bridge remains closed.

Here’s what we know so far.

Crash looked ‘absolutely surreal,’ governor says

The vehicle was traveling at an “extraordinarily high rate of speed” when it approached the border crossing around 11:30 a.m. and hit a barrier, Hochul said.

The impact sent the car soaring several feet into the air before it came crashing down into a Customs and Border Protection booth and burst into flames, Hochul said. She described footage of the incident as “absolutely surreal.”

An officer working in the booth was treated for minor injuries, she said.

The vehicle was “basically incinerated” and pieces of the wreck were scattered across more than a dozen checkpoint booths, the governor said.

Rickie Wilson saw the car flying past him “almost like a movie,” and for a moment, he thought it was a plane, the witness told CNN affiliate WKBW.

FBI investigated explosion as possible terrorist threat

In the aftermath of the crash, federal investigators scrambled to determine whether the incident was an act of terrorism. Within hours, officials shared preliminary findings and assured the public they hadn’t found any indication of terrorist motivation.

“But we will continue to stay vigilant. We will continue to make sure that the information we have is passed onto the public,” US Attorney Trini Ross of the Western District of New York said in a news conference.

The leaders of both the US and Canada were briefed on the incident as the investigation was underway.

The initial explosion triggered heightened security precautions around the region, including the evacuation of local government offices on the US side.

Buffalo Niagara International Airport closed to international arriving and departing flights but later lifted the restriction, according to the US Federal Aviation Administration. All cars coming into the airport were also being screened by bomb-detecting dogs, a Niagara Frontier Transportation Authority spokesperson said.

Amtrak temporarily suspended part of its cross-border route connecting New York to Toronto.

Officials investigating the crash had been looking into an individual but working through the Joint Terrorism Task Force did not initially find any concerning information, FBI Special Agent-in-Charge Matthew Miraglia said Wednesday afternoon.

“We do not have any derogatory information on this person that we’ve identified,” he said. “We’re scanning his social media, there’s nothing there. We’re still running a full investigation so that’s a preliminary assessment.”

By Wednesday night, the FBI announced it had concluded its investigation at the scene and turned the case over to the Niagara Falls Police Department as a traffic investigation.

CNN’s Pete Muntean, Raja Razek, Dave Alsup, Josh Campbell and Sabrina Souza contributed to this report.