Howard County police spokeswoman Sherry Llewellyn told the Associated Press the deaths of Rose Mayr and Elizabeth Nass, who died in the derailment just after midnight Monday in Ellicott City, near Baltimore, have been ruled accidental.
The cause of death was compressional asphyxia, a type of suffocation resulting from compression of the chest cavity.
Officials added that the two were found buried under coal but still seated on the edge of the bridge where they had just moments before taken Twitter photos of themselves and the view from the overlook.
The pair, both 19, were not hit by the train, Llewellyn said.
CSX and the National Transportation Safety Board are still investigating why 21 cars of an 80-car train left the tracks earlier this week as it approached its destination of Baltimore from Grafton, West Virginia.
One official told the AP earlier this week that determining a cause could take weeks.
So far, the two have determined that none of the three CSX employees who were on the train activated its emergency brakes, though they were automatically set when the derailment began.
Several other reports have indicated that the train was traveling just 25 miles per hour at the time.
“This will be a very wide-ranged investigation,” NTSB lead investigator Jim Southworth told the news service.
“[Investigators] will look into the maintenance of the track, the maintenance of the equipment, the maintenance of the locomotive – everything you can think of.”
He also said the two locomotives on the train did not leave the tracks and that the CSX crew “felt nothing, and they saw nothing” before the emergency brakes engaged.
The line in the area was expected to return to service Thursday, according to local news reports.