The last wrecked railcars from the deadly Amtrak accident were removed Friday as investigators tried to figure out why the train sped up from 70 mph to over 100 mph in the minute before it went into a sharp bend.
Brandon Bostian, the engineer whose handling of the train has emerged as a central element in the probe, has agreed to talk to federal accident investigators in the coming days, the National Transportation Safety Board said.
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Meanwhile, Amtrak CEO Joseph Boardman said in a letter on the railroad's blog Thursday that Amtrak "takes full responsibility and deeply apologizes for our role in this tragic event."
The derailment Tuesday night killed eight people and injured more than 200.
"With truly heavy hearts, we mourn those who died. Their loss leaves holes in the lives of their families and communities," Boardman wrote.
He said the railroad's goal is "to fully understand what happened and how we can prevent a similar tragedy from occurring in the future."
On Thursday, the NTSB said that the locomotive's video camera showed that in the last minute or so before the derailment, the Washington-to-New York train accelerated rapidly as it approached a curve where the speed limit is 50 mph.
The engineer applied the emergency brakes seconds before the wreck, but it was too late, investigators have said.
NTSB member Robert Sumwalt said it is unclear whether the speed was increased manually by the engineer.
So far, investigators have found no problems with the track, the signals or the locomotive, and the train was running on time, Sumwalt said.
Separately, the Philadelphia district attorney's office said it is investigating and will decide whether to bring charges.
Bostian's lawyer, Robert Goggin, told ABC News that his client suffered a concussion in the wreck and has "absolutely no recollection whatsoever" of the crash but had not been using his cellphone and had not been drinking or using drugs.
The last wrecked cars were pulled from the scene and were being taken on flatbed trucks to an Amtrak installation in Delaware for further examination.
Amtrak service on the heavily traveled stretch between New York and Philadelphia is expected to be suspended through Monday while the tracks and other equipment are repaired, the railroad said. Earlier, Amtrak said limited service was scheduled to resume on Monday.
The first funeral for the victims was held Friday morning. Services for Justin Zemser, a 20-year-old midshipman at the U.S. Naval Academy, took place on Long Island.
Six of the injured remained in critical condition but were expected to pull through.
Bostian, 32, graduated from the University of Missouri-Columbia with a bachelor's degree 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. He lives in New York City.
Friends said he talked about trains constantly while growing up and wanted to be an engineer or a conductor even back then.
"He would go on vacation and bring back subway maps," Stefanie McGee, a friend in Bostian's hometown of Bartlett, Tennessee, a suburb of Memphis. "He would go places with his family, and he would talk about the trains instead of the places."
Will Gust, a college fraternity brother of Bostian's, said he had "nothing but good things to say about Brandon."
"He is a very conscientious person, one of the most upstanding individuals that I know, just a really good-quality person," Gust said.
Kunzelman reported from Baton Rouge, Louisiana. Associated Press writers Heather Hollingsworth in Kansas City, Missouri, Adrian Sainz in Memphis, Tennessee, and Jennifer Peltz in New York contributed to this story.