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 an Amtrak train that investigators say barreled into a curve in Philadelphia on Tuesday night at more than 100 mph, or twice the speed limit. Eight people were killed in the derailment.

Investigators want to know why the train was going so fast. But Bostian refused to talk to police on Wednesday, authorities said. And investigators with the National Transportation Safety Board said they would give him a day or two to recover from the shock of the accident before talking to him.

His lawyer, Robert Goggin, told ABC News that Bostian 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.

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 always wanted to be a train engineer, a train 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 Tuesday, that job 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.

"Hold your head up," wrote a Facebook friend whose profile identifies him as an Amtrak engineer living in California. "Yes, it happened to you but it could have been any one of us and you are not alone."

More than 200 people were injured in the crash. 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.

The tragedy has led to new demands for the installation of technology known as positive train control, which uses GPS, wireless radio and computers to prevent trains from going over the speed limit.

Amtrak has equipped most of its heavily used Northeast Corridor with positive train control, but not the section where the accident happened.

On Thursday, Amtrak CEO Joseph H. Boardman vowed that positive train control will be installed along the entire Northeast Corridor by the end of 2015, the deadline set by Congress.

Amtrak carries 11.6 million passengers a year along the Northeast Corridor, which runs between Washington and Boston.

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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