The nine-car City of New Orleans, en route to Chicago, jumped the tracks Tuesday night near Flora. Its cars tumbled five or six feet off a trestle about 25 miles north of Jackson.
National Transportation Safety Board vice chairman Mark Rosenker would not speculate on the cause but said the FBI had examined the scene and found no reason to believe it was anything but an accident.
At a Wedneday evening briefing, Rosenkar said the train's data recorder showed its speed reduced from 78 mph to a dead stop at about 6:33 p.m. Tuesday, and investigators said it appeared that the engineer had pulled the emergency handle.
"We will know more about why he did that" on Thursday, when interviews with the crew were planned, he said.
The area has a history of derailments, and passenger Iris Giorgi said she heard a conductor say, "This is the worst part of the track" as the wheels screeched and the passengers cars rattled. Minutes later, Giorgi, a nurse from Glendora, Calif., was helping to tend the injured.
Four freight trains have crashed on the five-mile stretch near Flora since 1994. One, in 1997, was carrying hazardous chemicals, and 4,000 residents had to be evacuated.
NTSB investigators planned to collect blood and urine samples from the engineer and crew to test for drugs and alcohol.
Most of the injured were treated and released. One remained hospitalized in critical condition.
It was Amtrak's first passenger death since 2002, when an Auto Train derailed at Crescent City, Fla., killing four passengers and injuring more than 150 people.