The Amtrak train that derailed at a curve killing eight people was accelerating when it was supposed to be slowing down.
Why that happened has emerged as the central question surrounding the derailment, which sent more than 200 people to hospital on Tuesday in the worst US train wreck in nearly six years.
In the minute or so before the crash, the train sped up from 70mph until it reached more than 100mph at a sharp bend where the maximum speed is supposed to be 50mph, National Transportation Safety Board member Robert Sumwalt said.
He said it is unclear whether the speed was increased manually by engineer Brandon Bostian, who grew up obsessed with trains.
Investigators have found no problems with the track, signals or locomotive. Mr Sumwalt said the train, on a route from Washington to New York City, was on time as it left the station in Philadelphia a few minutes before the crash.
Investigators want to know why the train was going so fast, but Mr Bostian refused to talk to police on Wednesday.
Yesterday, Mr Sumwalt said the engineer had agreed to be interviewed by the NTSB and the meeting will take place in the next few days.
Separately, the Philadelphia district attorney’s office said it was investigating and will decide whether to bring charges.
And an Amtrak worker injured in the crash filed what is apparently the first lawsuit stemming from it, blaming Amtrak and seeking at least $150,000 in damages, his lawyer said.
Amtrak called the derailment “a terrible tragedy” and said it was co-operating fully with the NTSB and was responding with every resource it has available.
Mr Bostian’s lawyer, Robert Goggin, told ABC News that his client suffered concussion in the wreck, needed 15 staples in his head and has “absolutely no recollection” of the crash.
Mr Goggin said his client, who lives in New York, had not been using his mobile phone, drinking or using drugs.
As the death toll climbed yesterday with the discovery of what was believed to be the last body in one of the mangled carriages, Philadelphia Mayor Michael Nutter again appeared to cast blame on Mr Bostian, questioning why the train was going so fast.
Officials believe they have accounted for all 243 passengers and crew members thought to have been aboard, Mr Nutter said. He said 43 remain in hospital.
Amtrak, meanwhile, said limited train service between Philadelphia and New York should resume on Monday, with full service by Tuesday.
Amtrak carries 11.6 million passengers a year along the Northeast Corridor, which runs between Washington and Boston.
Mr Bostian was obsessed with trains while growing up, talked about them constantly and wanted to be an engineer or a conductor, friends said.
He graduated from the University of Missouri-Columbia with a bachelor’s in business administration and management in 2006. He became an Amtrak engineer in 2010, four years after landing a job as a conductor, according to his LinkedIn profile.
Mr Goggin said the engineer does not recall anything out of the ordinary and does not remember applying the emergency brakes, as investigators say was done. He said Mr Bostian’s mobile phone was off and stored in his bag before the accident, as required.
He said his client “co-operated fully” with police and told them “everything that he knew,” immediately consenting to a blood test and surrendering his mobile phone.