ELLICOTT CITY, Md. — They were seemingly ordinary tweets from two friends hanging out on a railroad bridge in their hometown, enjoying one last summer night together before heading back to college.

"Drinking on top of the Ellicott City sign," read one. "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 another tweet.

Minutes after the messages were shared on the social media site Twitter, a Baltimore-bound CSX freight train loaded with coal barreled down the tracks and derailed, killing the 19-year-old women and toppling railcars and coal onto the streets below of this historic Maryland community.

Investigators were still trying to figure out what caused the derailment. Witnesses heard squealing brakes and a thunderous crash around midnight Monday.

It wasn't clear whether the women's presence on the tracks had anything to do with the derailment. They were sitting on the edge of the bridge over Ellicott City's main street as the train passed a few feet behind them, Howard County police said, and their bodies were found buried under coal. 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 accessible from the picturesque downtown of Ellicott City, about 15 miles west of Baltimore, and generations of young people have played and partied along the tracks. The railroad was completed in 1830 and crosses over Main Street in the city's historic district, following the route of the nation's first commercial railroad, according to the Baltimore & Ohio Railroad Museum.

"We grew up running on those tracks," said Ellicott City native Bridgette Hammond, 25. "It's actually really beautiful up there."

Nass and Mayr were on the dance team at Mt. Hebron High School in Ellicott City, from which they graduated, and they 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 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 Tuesday afternoon, but friends confirmed they were hers and police said they were aware of the posts and looking into them.

Jill Farrell, who lives across the street from the tracks, said she heard what sounded liked squealing brakes and then a crash, followed by silence.

Benjamin Noppenberger was getting ready for bed 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.

Jim Southworth, investigator in charge for the NTSB, declined to speculate on a possible cause. He said the brakes were applied automatically when an air line used to pressurize the braking system was disconnected. He did not say what role, if any, the brakes may have played in the derailment.

"This will be a very wide-ranged investigation," Southworth said, adding that officials will "look into the maintenance of the track, the maintenance of the equipment, the maintenance of the locomotive – everything you can think of."

The crew of three – an engineer, a conductor and an engineer trainee – didn't see or feel anything unusual before the crash, Southworth said. They were not injured.

The train was equipped with video-recording devices that investigators will review to help them determine what happened. It was going about 25 mph but Southworth would not say whether that was an appropriate speed limit for the area.

CSX spokesman Bob Sullivan said that the train was traveling from Grafton, W.Va., to Baltimore. It had two locomotives and weighed 9,000 tons, he said. The first 21 cars of the 80-car train derailed.

Patrick Moran, an engineering consultant who lives near the bridge, told The Baltimore Sun that he went to the scene afterward and spoke with a man who identified himself as the train's conductor. Moran said he asked the man if he was all right, and the man said he had seen the women near the tracks and passed them but that then "the rail blew out," rail cars started tipping over and coal began spilling out.

Environmental officials responded because about 100 pounds of coal spilled into a tributary of the Patapsco River, a major Maryland waterway that parallels the tracks. Maryland Department of the Environment spokesman Jay Apperson said much more coal lay along the edge of the tributary, raising concerns it could boost the acidity of the water or otherwise threaten aquatic life.

The derailment also damaged some of Verizon's equipment, disrupting land-line telecommunications services to clients.

The problems reached all the way to the U.S. Navy base in Guantanamo Bay, Cuba, where pretrial hearings were delayed for a day for five men charged with orchestrating and aiding the Sept. 11 attacks because files on government servers were temporarily unavailable.

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Gresko reported from Washington. Associated Press writers Matthew Barakat in Ellicott City, David Dishneau in Hagerstown, Md., and Karen Mahabir in Washington contributed to this report.

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Online:

Mayr's Twitter feed: http://twitter.com/r0se_petals

Nass' Twitter feed: http://twitter.com/LizNassty

Loading Slideshow...
  • Maryland Train Derailment

    Officials inspect part of a CSX freight train that derailed alongside a parking lot overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities say the train, hauling coal from West Virginia to Maryland, derailed and fell from a bridge near Baltimore, killing two college students who were on the tracks. Howard County officials say 21 of the train's 80 cars flipped over around midnight Monday. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    Officials walk past a car that was destroyed by a CSX freight train that derailed while hauling coal overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    An official walks alongside part of a CSX freight train that derailed overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    Officials stand underneath a bridge where part of a CSX freight train derailed overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    An official photographs derailed train cars after a CSX freight train hauling coal derailed overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    An official walks past part of a CSX freight trail that derailed overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    An official inspects part of a CSX freight train that derailed alongside a parking lot overnight in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. The victims were Elizabeth Conway Nass, a student at James Madison University in Virginia, and Rose Louese Mayr, who attended the University of Delaware, according to Howard County police spokeswoman Sherry Llewellyn. They were both 19 years old. Police did not immediately say what the women were doing on the tracks. (AP Photo/Patrick Semansky)

  • Maryland Train Derailment

    Coal that spilled from a derailed CSX freight train, bottom, partially covers cars in a parking lot in Ellicott City, Md., Tuesday, Aug. 21, 2012. Authorities said two people not employed by the railroad were killed in the incident. The victims were Elizabeth Conway Nass, a student at James Madison University in Virginia, and Rose Louese Mayr, who attended the University of Delaware, according to Howard County police spokeswoman Sherry Llewellyn. They were both 19 years old. Police did not immediately say what the women were doing on the tracks. (AP Photo/Patrick Semansky)