The evidence that a bad industrial accident had become a human tragedy was caught in the glare of a police spotlight pointed up at the railroad bridge in Ellicott City.

Sirens were still screaming as other officers raced to the scene, minutes after a coal train derailed Tuesday just after midnight. Dust rose like smoke from the coal dumped by 21 upturned rail cars. The stunned crew of three began to climb down from their locomotive to survey the twisted wreckage.

But the true tragedy of the moment was captured in a pencil of light trained on the bridge.

Two 19-year-old women had been sitting on the ledge of the railroad trestle as the train roared by. When the rail cars inexplicably began to derail like a row of dominoes, the one that turned on its side behind the women missed them by inches. The coal — about 110 tons of it — did not.

It buried them where they sat, cascading past them to the street below, leaving just enough evidence of their presence to show in the spotlight from the officer below.

Investigators will gather evidence for another day or two in the accident that killed Elizabeth Nass and Rose Mayr. They will piece the track together in a parking lot below the rail bed to look for clues, and then they will take all that they have collected to a laboratory to figure out the cause of the derailment.

The two locomotives and the 59 coal cars that remained upright had already been removed Wednesday, as were most of the 21 cars that derailed. Officials with CSX, owner of both the train and the rail bed, said they hoped that operations on the single-track line into Baltimore would resume by late Wednesday or early Thursday.

Gary Sease, the rail company’s communications director, said environmental consultants had been brought in to evaluate the spill’s impact on the adjacent Patapsco River.

“It doesn’t appear there is much coal in the river,” he said.

Jim Southworth, lead investigator for the National Transportation Safety Board, said a review of the train’s data recorder confirmed statements given by the crew members to police — that they had not applied the brakes on the train.

The crew members also told police that they never saw the two women sitting on the bridge beside the tracks, Southworth said. The fact that they were not in the path of the train and that the engineers neither saw them nor applied the locomotive’s brakes suggests they were innocent victims.

The crew members were scheduled for more interviews with Southworth and other NTSB investigators.

Ellicott City train derailment (Gene Thorp/The Washington Post)

Southworth said that a broken line in the air brakes apparently triggered automatic braking in each of the 80 coal cars, but he said it was unclear whether that caused the derailment or whether a flaw in the track was a factor.

“We’re looking at all of that,” he said. “We’re not going to do anything hypothetical at this time. We never speculate.”

Southworth said that working on a rail bed wrapped around the historic district of Ellicott City made the investigation more challenging than most derailments.

“This is a well-orchestrated industrial ballet,” he said. “It’s an in­cred­ibly challenging location; it calls for careful, deliberate work.”

Just before the accident, Nass and Mayr posted photos and several messages from atop the bridge that sits between the foot of Main Street and the river.

One showed their bare feet dangling over the edge of the bridge as they sat just above the words “Ellicott City,” painted on the side of the bridge that is a portal to the community.

“Drinking on top of the Ellicott City sign,” Nass had tweeted as the train was about eight miles away, moving in their direction.