Investigators were checking videos, track conditions and maintenance records to learn whether two young women sitting on a railroad bridge over the town's main street contributed to the Monday night crash or if their presence was just a tragic coincidence.
National Transportation Safety Board investigator Jim Southworth wouldn't speculate on the cause of the derailment.
"This is just not the time for any kind of analysis," he said Wednesday. "This is purely fact-finding."
So far, investigators have determined the emergency brakes were applied automatically - not by the three-man crew - on Monday around midnight, but they don't know why the train jumped the tracks.
Southworth said the train's two locomotives did not derail. Investigators planned to remove the tracks from the crash site and reassemble them in a nearby parking lot for inspection.
Cleanup of area continued Wednesday. Nineteen of the 21 derailed cars had been removed, but it could be another two days before the area is clear for traffic through the narrow historic area. Southworth called the work a "well-orchestrated industrial ballet."
Tweets and photos from the two 19-year-old college students chronicled some of their final moments together as they enjoyed a summer night together before they were to headed back to school.
"Drinking on top of the Ellicott City sign," read one tweet. "Looking down on old ec," read another.
Accompanying photos showed their view from the bridge and their bare feet, one with painted blue toenails, dangling over the edge. "Levitating," read the tweet.
The women were sitting on the edge of the bridge with their backs to the tracks as the train passed a few feet behind them, Howard County police said, and their bodies were found buried under coal dumped from the train cars. Authorities said they needed to do autopsies before their cause of death could be determined.
The victims were identified as Elizabeth Conway Nass, a student at James Madison University in central Virginia and Rose Louese Mayr, a nursing student at the University of Delaware.
The railroad is easily accessed from the picturesque downtown of Ellicott City, which is about 15 miles west of Baltimore, and generations of young people have played and partied along the tracks.
The original stone bridge was built around 1830, according to Courtney Wilson, executive director of the Baltimore & Ohio Railroad Museum in Baltimore. He said it was replaced after an 1868 flood with an iron truss bridge that provided wider lanes for vehicles passing beneath. That structure was replaced around 1930 with the current steel span.
Shelley Wygant of the Howard County Historical Society said the edge of the bridge on which the women sat, facing the Patapsco River, is at least two feet from the single set of railroad tracks. The side of the bridge facing the town has a wider platform, she said.
Still, "I don't think anybody would want to be up there when trains go by," Wygant said.
"I've been up there to hang banners and things like that and thinking, 'I hope a train doesn't come,'" she said.
Nass and Mayr were graduates of Mt. Hebron High School in Ellicott City, where they were on the dance team, and planned to finish college in 2014, according to friends and their Facebook pages.
One of Nass' sorority sisters, Donya Mossadeghi, called her "a joy to talk to" and someone who "would never say a bad thing about anybody." Nass made the dean's list in the fall of 2010 and 2011, according to a university spokesman, and another friend said she was studying special education.
Tori Mace, of Ellicott City, knew Mayr through mutual friends. "She was really fun, really friendly," Mace said.
A person who answered the telephone at Nass' home declined to comment, as did a family member who answered at a number listed for the Mayr family.
The pictures and tweets from Mayr were no longer publicly available, but friends confirmed they were hers and police said they were aware of the posts and looking into them.
Benjamin Noppenberger was getting ready for bed late Monday when he and his wife heard what sounded like gunshots. They waited about 10 minutes before going outside.
"We could see all the cars that fell over. I just saw catastrophe," he said.