VALHALLA, N.Y. (CBSNewYork) — A team of federal investigators arrived Wednesday at the Westchester County site of a crash that authorities have called the deadliest in Metro-North’s history.

As CBS2’s Lou Young reported, federal investigators gathered around the crumpled Mercedes sport-utility vehicle as they arrived. It had been stuck in traffic at the Commerce Street grade crossing in Valhalla when the fast-moving Harlem Line train obliterated it at 6:40 p.m. Tuesday, eventually killing the driver and five men aboard the train.

“That train had so many flames in it; it was so engulfed. The inside of that first car is just melted and charred with the third rail going straight through it. So the scene is just horrific and unimaginable,” Westchester County Executive Rob Astorino said Wednesday.

Astorino examined the wreckage following the accident.

Meanwhile, Gov. Andrew Cuomo announced late Wednesday that full service will resume on the Harlem Line of the Metro-North Railroad Thursday morning.

The first train to operate over the Commerce Street crossing where the accident happened will be the 4:26 a.m. departure from Southeast, Gov. Andrew Cuomo announced Wednesday. The train will arrive at Grand Central Terminal at 5:30 a.m.

Cuomo warned that Metro-North customers should expect delays Thursday morning, as there is still an active work zone at the site of the accident.

Speaking to “CBS This Morning” Wednesday, Cuomo said of the wreck, “This was as gruesome as I have seen.”

“It’s really inexplicable,” Cuomo added in comments to WCBS 880. “Everybody wants to know exactly what happened, so that if something can be corrected, we do correct it.”

A view of the front train car showed where the electrified third rail went through the vehicle, and then into the first car of the commuter train — setting everything ablaze.

Bodies were so badly mangled that emergency workers first thought there were seven fatalities — until the Westchester County Medical Examiner’s office told them there were just six people killed.

“This is the worst in my history. I’ve been doing this 10 years, 11 years. It’s the worst scene I’ve been to,” one EMS worker said.

Hundreds of commuters in the trailing cars realized the horror upfront, only when they were evacuated.

At the railroad crossing where the incident happened, the gates remained down late Wednesday afternoon. Lights continued to flash as investigators worked through the wreckage.

National Transportation Safety Board board member Robert Sumwalt said experts in areas of signals, crossing gates, medical records, data recorders, emergency response, tracks, highway factors, fire science and mechanics will investigate.

Sumwalt said in a late Wednesday afternoon news conference that he arrived during the 10 a.m. hour and surveyed the scene.

“We intend to find out not only what happened, but we want to find out why it happened,” Sumwalt told reporters. “And our sole purpose for being here is to find out what happened so that we can offer recommendations to hopefully keep this from happening again.”

Sumwalt said the exact speed of the train at the point of the collision should be reportable by Thursday, but investigators have yet to verify the information. The SUV was pushed 1,000 feet at the point of collision, he said.

For about 400 feet, the third rail started breaking apart in eight-foot sections and piercing the floor of the first rail car. At least one piece also penetrated the second rail car, Sumwalt said.

The entire interior of the first car was burned out, Sumwalt said. The initial investigation suggests the fire was fueled by gasoline from the SUV, Sumwalt said.

Following the crash, the heat of the fire-melted metal essentially welded the stricken SUV to the underside of the commuter train.

Experts said if not for the third rail punching up into the train car, the SUV driver might have been the only one killed in the accident, Young reported.

“Was the electrical power to the third rail – was it interrupted when it started to break apart as it is designed to do?” Sumwalt said.

As CBS2’s Jessica Schneider reported, investigators on Wednesday were also still trying to determine why the SUV ended up in the crossing. Sumwalt noted that there had been a traffic detour in the area prompted by an earlier crash on the nearby Taconic State Parkway.

He said investigators will be at the scene for five to seven days documenting “perishable evidence,” that is, evidence that can go away with the passage of time.

The NTSB will also look at the adequacy of the emergency exits on board, and the crashworthy strength of the rail cars.

Anyone who can help the NTSB with witness information should send an e-mail to witness@ntsb.gov, Sumwalt said.

WATCH: NTSB Briefing On Metro-North Crash | PHOTOS: Deadly Metro-North Accident

Crews late Wednesday afternoon hauled the train from the scene and were to take it to a storage facility. The SUV was removed from the scene earlier.

Meanwhile, the engineer and conductor survived and investigators will also be able to gather information from them, Astorino said.

“They got out so we’ll be able to hear from them exactly what happened, certainly from the engineer,” he said. “But I think we’re going to have to leave that up to the NTSB to see whether there was signal failure or something wrong with the track as opposed to driver error.”

Early indications were that the motorist who was killed made a serious mistake in heavy traffic.

“Apparently, the gate went down on the car, and she got out to put the gate up, and at that point, got back in the car and started driving, and she was hit by the train,” Astorino said.

The black box-type recording devices on the train and in the crossing equipment should help move the investigation along, officials said.

Meanwhile, Greenburgh Town Supervisor Paul Feiner confirmed to CBS2 that Ellen Brody was the driver of the SUV. Feiner said Brody, 49, was a mother of three and a “wonderful, warm person.”

Ellen Brody, the driver of an SUV struck by a Metro-North train on Feb. 3, 2015. (credit: Image via Facebook)

Ellen Brody, the driver of an SUV struck by a Metro-North train on Feb. 3, 2015. (credit: Image via Facebook)

Feiner knew Brody and said she was not the type to try to beat the crossing arm and put other lives at risk.

“She is just a very responsible, level-headed person,” he told WCBS 880’s Alex Silverman. ” … I don’t think she was a careless person.”

One of the other victims was Eric Vandercar, 53, a senior managing director with Mesirow Financial, the company said. He was a father of two, 1010 WINS’ Derricke Dennis reported.

“Eric was not only a pillar in our industry, he was a great partner and friend to many,” Mesirow Financial said in a statement. “Losing him is a huge loss, personally and professionally. Our entire Mesirow family is hurting and our deepest sympathies are extended to his wife, Jill, and their family.”

Eric Vandercar was killed when the Metro-North train he was riding in struck an SUV on Feb. 4, 2015. (credit: Mesirow Financial)

Eric Vandercar was killed when the Metro-North train he was riding in struck an SUV on Feb. 4, 2015. (credit: Mesirow Financial)

Walter Liedtke has also been confirmed as among the fatalities, CBS2 has learned.

According to an online biography of Liedtke, he was a curator of European paintings and organized exhibitions at The Metropolitan Museum of Art.

Walter Liedtke of the Metropolitan Museum of Art was among those killed in the Metro-North accident in Valhalla on Tuesday, Feb. 3. (Credit: Metropolitan Museum of Art)

Walter Liedtke of the Metropolitan Museum of Art was among those killed in the Metro-North accident in Valhalla on Tuesday, Feb. 3. (Credit: Metropolitan Museum of Art)

Late Wednesday afternoon, the Hackley School – an elite private school in Tarrytown – identified a fourth victim of the crash as Joseph Nadol. He was a father of three students at the school, CBS2’s Tony Aiello reported.

Nadol, 42, was an analyst for JPMorgan and lived in Ossining.

Joseph Nadol

Joseph Nadol of JPMorgan was among those killed in the Metro-North accident in Valhalla on Tuesday, Feb. 3. (Credit: JPMorgan)

“Our thoughts and support are with Joe’s family during this difficult time,” a JPMorgan representative said in a statement.

A fifth victim was identified late Wednesday as Aditya Tomar, 41, of Danbury, Connecticut, according to the Danbury Mayor’s office.

A sixth victim’s identity had not been confirmed late Wednesday.

Astorino said with the exception of one of the victims, all of the bodies were severely burned.

Authorities said the number of injured was up to 15, seven of them seriously.

Astorino said the dead are being identified through dental records.

“Fortunately, the majority of the patients on the train were not seriously injured,” Emergency Room Director Dr. Ivan Miller said.

Initially, officials said the SUV was a Jeep Cherokee, but authorities later realized that it was a Mercedes, Metropolitan Transportation Authority spokesman Aaron Donovan said Wednesday.

Officials earlier explained in part how the electrified third rail on the tracks became dislodged after the impact and pierced the floor of the front train car.

“The third rail stops at the grade crossing, and so that’s where the contact with the automobile was made and it entered through the automobile and up through the floor of the car,” MTA President Thomas Prendergast explained.

The SUV and the front car of the train burst into flames, sending hundreds of passengers scrambling for safety.

Astorino said he was amazed anyone got off the train alive.

“That train had so many flames in it; was so engulfed, the inside of that first car is just melted and charred,” he said. “The scene must have been horrific and unimaginable.”

For most on board, the full horror revealed itself only as they began to evacuate.

“The train came to an abrupt halt,” said passenger Sally Barton, of Putnam County. “We weren’t getting any information, but we knew that something bad was going on because there were lots of police cars, firemen.”

“We felt a little bit of a jolt,” another rider told 1010 WINS’ Glenn Schuck. “I was in the next to last car. I wasn’t sure if maybe we hit a deer — didn’t know what was happening and didn’t even know to what extent. When we were evacuating, you could see all the smoke coming from the train.”

Chris Gross, 24, of Somers, told WCBS 880’s Sean Adams he was riding in the first few rows of the first car when the collision tossed him from his seat. Within seconds, there was fire.

“Flames were about a foot from my head,” he said. “When I fell, people fell on top of me.”

Gross said he saw catastrophic injuries. Another man opened an emergency exit and they ushered the walking wounded off the burning train.

“I thank God I have angels looking out for me right now,” he said.

Gross told CBS2’s Young he was not sure when he’d be able to ride the rails again – and he was not alone in that sentiment.

“I don’t really get a lot of sleep, so I want to go home. I want to go to sleep right now. I just want to try and calm down,” Gross said.

Astorino said mental health experts are available for people who need it – whether friends and family of those killed or injured, or survivors who made it out alive.

“I think for most people, you have to move on with some sort of normalcy, but that’s going to take time from people,” he said late Wednesday afternoon.

In the area of the crash, the Harlem Line runs alongside the Taconic Parkway. An earlier accident had forced traffic off the Taconic onto local roads in bumper to bumper traffic, CBS2’s Young reported.

Locals say the narrow grade crossing gates give motorists plenty of warning.

“Usually, what happens the lights flash first, the bells ding then the arms come down,” Valhalla merchant Antonella Oddo told Young. “You have that little time frame, like seven or eight seconds, and then you usually hear the horn and the train comes through.”

The MTA said commuters should expect delays and service changes as a result of the crash. Astorino said the train must remain on the tracks as the NTSB investigates.

In addition to the NTSB, the Federal Railroad Administration is also investigating, Acting Administrator Sarah Feinberg said.

“We will conduct a thorough investigation to determine the factors that contributed to this accident,” Feinberg said in a statement. “Safety must be every railroad’s absolute top priority and we will establish what lapses, if any, occurred and order any necessary corrective actions.”

Sen. Charles Schumer, D-N.Y., said it’s too early to point fingers, but expects a full investigation.

Sen. Schumer told WCBS 880’s Connecticut Bureau Chief Fran Schneidau investigators have indicated the train was traveling just under 60 miles an hour when it hit the car at the crossing.

“Obviously, there are a whole lot of questions that I and many others will ask in the days to come,” he said.

Sen. Richard Blumenthal, D-Conn., also wants answers.

“The real question is what caused this horrendous, probably preventable incident that reflects further on the need for safety and reliability in this railroad,” he said. “Apparently there have been other accidents at this site, which leads me to think the incident could have been preventable.”

Tuesday’s crash is the latest in a string of recent incidents involving Metro-North trains.

In December 2013, a derailment in the Bronx killed four people and injured more than 60.

In May 2013, two Metro-North trains collided in Bridgeport, Connecticut, injuring more than 70 people.

Just last Wednesday, two minor derailments happened within hours of each other, one near Grand Central Terminal. No one was hurt, but several tracks were out of service.

On Monday night, a train broke down in Pelham, stranding hundreds of commuters for hours in dark and freezing conditions.

The FRA said in a report to Congress in March of last year that Metro-North allowed safety to erode while pushing to keep its trains on time.

The railroad has since pledged to make safety its top priority.

“We want Metro-North’s customers to know that they can remain confident that their safety, and the safety of our employees, is always the first priority in everything we do,” Metro-North President Joseph Giulietti said in a statement Wednesday. “We will work closely with the NTSB and local officials to determine the exact cause of this tragedy and work to ensure such incidents are not repeated.”

Prendergast said Wednesday the MTA is “tremendously saddened by this tragic accident.”

“The entire MTA family’s thoughts are with the relatives and loved ones of the victims of last night’s tragedy,” he said in a statement.

Metro-North has established a family assistance center at the Office of the Westchester County Medical Examiner at 10 Dana Road in Valhalla.

Information also is available at 800-METRO-INFO (800-638-7646).