Federal investigators on Monday are expected to release a trove of evidence in the May 12, 2015, Amtrak derailment in Philadelphia that killed eight commuters and injured more than 200.
Among the key mysteries that the materials may help answer: Why did the train take a sharp curve north of a Philadelphia station at twice the speed limit?
The documents, expected to run to more than 2,000 pages, will include black box data and transcripts of interviews with Train 188's engineer, Brandon Bostian, as well as those of other crew members and first responders.
The interviews could provide the most detailed view yet of Bostian, the 32-year-old engineer running the train last May when it sped to 106 m.p.h. before hurtling off the tracks in Frankford Junction, Pa.
Bostian's lawyer, Robert Goggin, has said the engineer does not remember the crash, The Philadelphia Inquirer reported. Bostian did not agree to a formal interview with police, and he has said little since the incident.
A few days after the crash, Bostian told the National Transportation Safety Board (NTSB) that he did not recall anything after ringing the train's bell as he passed through the North Philadelphia station, about three miles before the curve.
The day after the crash, Goggin told ABC News that Bostian recalled the train was "pulling into speed-restricted track," but that he did not remember activating the emergency brake. He said Bostian was not under the influence of drugs or alcohol.
NTSB has said that Bostian was not using his cellphone for calls, texting, or data at the time, though officials did not rule out other uses, such as an app. The board was analyzing Bostian's phone data.
Goggin has said the phone was in Bostian's bag at the time.
NTSB has already identified excessive speed as a key factor in the crash. The train was accelerating out of an 80 mph speed zone when it should have been slowing to 50 mph for the curve, investigators have said.
Amtrak installed an automatic speed control at the curve within days of the derailment, as it had in Boston in 1990, after a train entered a 30 mph curve near Back Bay Station at 76 mph and derailed into a commuter train. The railroad has since enabled speed technology for all but a small portion of the 450-mile Northeast Corridor, the Associated Press reported.
Early in the investigation, the NTSB focused on whether the train had been hit with a rock or other projectile minutes before the crash. The left-side of the locomotive's windshield had a grapefruit-sized fracture. The operator of a commuter train running along the same tracks reported being hit and passengers on another Amtrak train said something struck their train.
Monday's release will include the bulk of information that investigators will use to try to draw conclusions about what happened and what can be done to make travel safer and crashes less deadly. That analysis is expected to conclude this spring.
Former NTSB Chairman Jim Hall described Monday’s expected document release as "just the facts."
"This is the final step before you move into the analysis," he said.