Brandon Bostian was obsessed with trains while growing up, talked about them constantly and wanted to be an engineer or a conductor.

"He would go on vacation and bring back subway maps," Stefanie McGee, a friend from Tennessee, recalled Thursday. "He would go places with his family and he would talk about the trains instead of the places."

Bostian's teenage dreams would come true. But now, at 32, the Amtrak engineer finds himself at the very center of the investigation into the nation's deadliest train wreck in nearly six years.

He was at the controls of a train that investigators say entered a sharp bend at 106 mph, or twice the speed limit. Eight people were killed and more than 200 injured in the derailment Tuesday night in an industrial section of Philadelphia.

In yet another curious turn in the investigation, Robert Sumwalt of the National Transportation Safety Board said Thursday that the train sped up in the last minute or so before the wreck, going from 70 mph to over 100 mph.

He said it is not clear yet whether the speed was increased manually. So far, he said, investigators have found no problems with the track or the signals.

Investigators want to know why the train was going so fast. But Bostian refused to talk to police on Wednesday, authorities said. On Thursday, Sumwalt said that Bostian had agreed to be interviewed by the NTSB and that the meeting will take place in the next few days.

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 crash and has "absolutely no recollection whatsoever of the events." Goggin also said Bostian had not been using his cellphone, drinking or using drugs.

As the death toll climbed on Thursday with the discovery of what was believed to be the last body in one of the mangled railcars, Mayor Michael Nutter again appeared to cast blame on Bostian, questioning why the train was going so fast.

"I don't think that any commonsense, rational person would think that it was OK to travel at that level of speed knowing that there was a pretty significant restriction on how fast you could go through that turn," Nutter said.

Officials believe they have now accounted for all 243 passengers and crew members who were thought to have been aboard, Nutter said.

Forty-three remained hospitalized Thursday, according to the mayor. Temple University Hospital said it had six patients in critical condition, all of whom were expected to pull through.

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.

Bostian graduated from the University of Missouri-Columbia with a bachelor's in business administration and management in 2006, the university said. He became an Amtrak engineer in December 2010, four years after landing a job as a conductor, according to his LinkedIn profile. He lives in the Forest Hills section of Queens, in New York City.

Old friends and college classmates described him in glowing terms.

"I have nothing but good things to say about Brandon," said Will Gust, who belonged to the Acacia fraternity with Bostian at the University of Missouri. "He is a very conscientious person, one of the most upstanding individuals that I know, just a really good quality person."

McGee, the friend who is now the city clerk in Bostian's hometown of Bartlett, a suburb of Memphis, said he "talked about trains constantly" and always wanted to be an engineer or a conductor.

Bostian met up with college friends a few years ago in New York and told them he was working on trains.

"Oh yeah, he loved his job," said Justin Scott, another fraternity member with Bostian.

On an online forum for train enthusiasts called trainorders.com, a user who signed at least two of his posts with "Brandon Bostian" or simply "Brandon" commented on a wide range of industry issues, including safety. A couple of posts under the handle "bwb6df" lamented that railroads hadn't been fast enough to adopt "positive train control," GSP-guided technology that can prevent trains from going over the speed limit.

"They have had nearly a hundred years of opportunity to implement SOME sort of system to mitigate human error, but with a few notable exceptions have failed to do so," the writer posted in 2011.

The same user said in 2012: "It shouldn't take an act of Congress to get industry to adopt common-sense safety systems on their own."

It is unclear whether the author of the train-safety posts was, in fact, Bostian. In a message posted Wednesday, the site's administrator refused to release any information, citing privacy reasons.

Amtrak has equipped most of its heavily used Northeast Corridor with positive train control, but it was not in operation along the section where the accident happened because it was still undergoing testing, CEO Joseph Boardman said.

However, on Thursday, Boardman vowed that the technology will be in operation along the entire Northeast Corridor by the end of 2015, the deadline set by Congress.

On Tuesday, the job Bostian loved so much had him operating Amtrak's Train 188 from Washington to New York.

"He remembers coming into the curve. He remembers attempting to reduce speed and thereafter he was knocked out," said Goggin, his attorney. But 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 Bostian's cellphone was off and stored in his bag before the accident, as required. Goggin said that his client "cooperated fully" with police and told them "everything that he knew," immediately consenting to a blood test and surrendering his cellphone.

Within hours of the wreck, Bostian's Facebook profile picture was changed to a black rectangle.

"I imagine he is holding onto this pretty heavily," said Scott, his fraternity brother.

Friends who seemingly knew about his role in the crash before his name publicly surfaced rallied to his side online. A Facebook friend whose profile identifies him as an Amtrak engineer living in California assured Bostian "it could have been any one of us."