PHILADELPHIA -- Amtrak engineer Brandon Bostian remains at the center of the investigation into Tuesday night's derailment in Philadelphia, which killed eight people and left more than 200 injured in the nation's deadliest train wreck in nearly six years.
On Thursday, National Transportation Safety Board member Roberat Sumwalt said in the minute or so before the crash, the train sped up from 70 mph until it reached 106 mph.
The maximum speed at that spot is supposed to be 50 mph.
"Just before entering the curve is when the engineer applied the engineer induced braking, to put it into emergency braking," Sumwalt said at a news conference Thursday afternoon.
According it Sumwalt, it remained unclear whether the speed was increased manually by Bostian. He said investigators have found no problems with the track, signals or locomotive.
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.
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."
Bostian has submitted a blood sample to test for the presence of drugs or alcohol. Authorities will also examine his cell phone records, although his attorney said he was not under the influence or using his phone prior to the wreck.
Authorities said Bostian refused to talk to police on Wednesday. Thursday evening, Sumwalt said Bostian had agreed to be interviewed by the NTSB and the meeting will take place in the next few days.
Philadelphia Mayor Michal Nutter said Thursday city police officers learned little from Bostian during questioning after the accident.
"I believe it was a short interview in which he apparently indicated that he did not want to be interviewed," Nutter said.
For the second day, Nutter 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.
In addition to the NTSB, the Philadelphia district attorney's office is also investigating the crash. When asked by CBS News if criminal charges were possible, Nutter responded that the question was premature.
"The premise of your question doesn't allow me to answer it," Nutter said. "That is a huge 'if.' That is way down the line, and I cannot address that kind of issue... I didn't rule it in, I didn't rule it out, I can't answer the question."
Bostian, 32, 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.
In social media postings, a user who appears to be Bostian was often critical of the railroad industry for failing to implement safeguards against human error.
One posting from 2011 read, "At any point over the previous eighty years the railroad could have voluntarily implemented some form of this technology."
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.
However, on Thursday, Amtrak CEO Joseph H. Boardman vowed that the technology will be installed along the entire Northeast Corridor by the end of 2015, the deadline set by Congress.
Old friends and college classmates described Bostian in glowing terms, saying he 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."
"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.
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."