Late last night, an Amtrak train on one of the line’s most popular routes derailed in Philadelphia, throwing several cars and the engine off the tracks, killing at least six people and sending victims to six different area hospitals. At the moment, no one has any answers on what caused the derailment, but it’s the question on everyone’s minds:

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At least five people died when an Amtrak train bound for New York City derailed in Philadelphia Tuesday, Philadelphia Mayor Michael Nutter said, with six cars overturning and the engine separating from the rest of the train.

Amtrak reported that there were approximately 238 passengers and five crew members on board. Dozens of passengers have been taken to local hospitals for injuries.

“It is an absolute disastrous mess,” Nutter said this evening. “Never seen anything like this in my life.”

Five people died on the scene; a sixth person died later. Initially, the reports showed six critical cases and 43 other hospitalizations, but it’s not clear what the injury count is at the moment. One of the ad-hoc rescuers was fellow passenger and former Congressman Patrick Murphy (D-PA), who got interviewed by both ABC and CBS:

“It just happened so fast. Obviously a lot of debris, lights went out … a lot of screaming,” former Rep. Patrick Murphy said. He was on board when the train derailed.

Murphy, an Iraq vet, wasn’t injured, so he started helping those around him who were, reports CBS News correspondent Jericka Duncan.

“I just stayed back and told the people who were bleeding to put some pressure on the wounds that they were bleeding from because you don’t want to see those people bleed out,” said Murphy, who served in Congress as a Democrat from Pennsylvania’s 8th district from 2007 to 2011.

His military training came through in the moment when he didn’t want to leave anyone.

“We have an ethic in the military, you know, we leave no one behind and I wasn’t going to climb out when there were people still hurting,” Murphy said.

CBS interviewed some of the other passengers, who told the story of the derailment from their perspective:

The Department of Transportation and Philadelphia mayor Michael Nutter emphasized that no one knows the cause of the derailment yet, although that hasn’t stopped people from blaming Republicans on Twitter:

The cause wasn’t immediately known.

“We do not know what happened here. We do not know why it happened,” Nutter said. There was no indication the derailment was a result of an impact with another train, he said.

So far, there’s nothing to indicate the incident was an act of terrorism.

The NTSB has sent a “go team” to the site to get some of those answers. They will catch one break — the engineer and conductor both survived the crash:

Federal investigators are headed to Philadelphia in a bid to determine what caused an Amtrak train to derail in Port Richmond, killing at least six people and injuring dozens more.

A National Transportation Safety Board “Go Team” is scheduled to arrive at the crash scene later Wednesday morning. The Federal Railroad Administration said it also was sending at least eight investigators to the scene of what is believed to be the deadliest crash on the Northeast Corridor since 16 were killed when an Amtrak train collided with a freight train near Baltimore in 1987. …

Amtrak Train 188, bound to New York from Washington with 238 passengers and five crew members aboard, jumped the tracks just before 9:30 p.m. on a curve in a section of the Northeast Corridor known as Frankford Junction.

The area is normally under a speed restriction, requiring trains to slow down as they approach. Determining the speed of Train 188 at the time of the accident will be part of the investigation.

It’s best not to leap to conclusions without all of the data. The NTSB will probably issue some public statements in the next few days about preliminary findings, perhaps just to eliminate some of the more imaginative theories that always arise in the public sphere after events of this kind. It will take a long time to get a definitive answer, and Americans will have to remain patient while investigators do their jobs.