In the seconds before Amtrak train No. 188 derailed at Frankford Junction, the train's speed surged from 70 m.p.h. to 102 m.p.h. - more than twice the speed limit on the dangerous curve, the National Transportation Safety Board announced Thursday.

Just before the crash, with the train traveling at 106 m.p.h., the train's engineer, Brandon Bostian, hit his emergency brakes, NTSB officials said. But it was too late.

Two days after the deadliest train crash on the Northeast Corridor in three decades, the revelations on the train's acceleration - while providing the most detailed account yet of the moments before the derailment - raised new questions about the 32-year-old engineer's actions.

Officials involved in the investigation told The Inquirer that Philadelphia police earlier Thursday had obtained a search warrant for Bostian's cellphone records. Those records would help investigators determine whether he could have been distracted - whether the phone had registered any activity in the moments before the crash.

NTSB officials said they had not yet determined why the train accelerated so rapidly. The speeds were recorded by a track image video recorder on the front of the train.

NTSB board member Robert Sumwalt said that he would "let [the figures on the crash] stand on their own."

He said it was unclear whether the engineer manually increased the speed - but that only the engineer could do so. He said that he did not think that the engineer crashed the train deliberately.

"If we thought that, we wouldn't be here, because that would be a criminal act," he said. "And we don't investigate criminal acts."

Bostian, who suffered a concussion in the derailment, has declined to give a formal statement to Philadelphia police investigating the crash, and told them in a brief hospital interview shortly after the crash that he could not recall most of the incident.

He has agreed to be interviewed by the NTSB, which is not a law enforcement agency, officials said.

Mayor Nutter said it was "important" that Bostian had agreed to an NTSB interview, "for whatever he can recall."

"The 243 people on that train, and certainly the families of the eight who died - they deserve answers," he said.

After the NTSB announced the acceleration issue, Nutter said: "You put all this information together. All it says is something went drastically wrong in that engine with the engineer."

Sumwalt said the NTSB wants to review the train's data recorder, which will reveal throttle positions, before determining whether the engineer manually accelerated. The engineer would have had to move the throttle to speed up.

Investigators on Thursday worked to rule out as many possible contributing factors to the crash as they could: mechanical failures, for example, or the presence of a medical condition that could have affected Bostian's driving.

The NTSB said it has reviewed records of the pre-inspection of the train and its brakes before it left Washington on Tuesday and found no anomalies.

Police are awaiting a toxicology report on blood given voluntarily by Bostian shortly after the crash, sources said. Sources said he displayed no obvious signs of impairment that night, such as a smell of alcohol.

Bostian's lawyer, Robert Goggin III, appeared on ABC News on Thursday morning and said that his client had been interviewed for six hours by detectives and was fully cooperating with the investigation. He said Bostian suffered a concussion and was unable to recall the crash or applying the emergency brakes.

"The next thing he recalls is being thrown around, coming to, finding his bag, getting his cellphone and dialing 911."

Goggin described Bostian as "distraught." The attorney could not be reached Thursday for comment.

Officials familiar with the investigation countered that description, and said that so far the engineer's contact with police had been perfunctory, adding that he had refused to speak to police in any detail about the crash. They said Bostian had spent his time at the East Detective Division waiting for his lawyer to arrive, not speaking with investigators. The only time he was questioned by detectives, they said, was during a brief conversation at Einstein Hospital.

Nutter told reporters that Bostian had told detectives he did not want to be formally interviewed.

"And he doesn't have to be interviewed if he doesn't want to be at this particular stage," Nutter said.

Before Bostian left East Detectives with his attorney early Wednesday afternoon, police officials consulted with the Philadelphia District Attorney's Office on whether charges could be pressed, sources familiar with the investigation said.

By then, preliminary information had indicated the train had been traveling at dangerous speeds.

The decision was made that there was not enough evidence yet collected in the case, sources said. Any decision on whether Bostian should be charged will lie with the District Attorney's Office.

Bostian was being treated for a concussion and a head laceration when two Philadelphia police detectives approached him at Einstein, hours after the crash, sources said.

They were part of a team of city investigators, sent two by two to every hospital in the area, trying to account for the passengers and crew aboard the train that now lay twisted and mangled in a Port Richmond industrial yard.

They asked him the questions they asked everyone, said the sources.

His name; his date of birth; his address; and where he had been on the train.

Bostian, of Queens, N.Y., told them he had been driving it. And that he remembered almost nothing about the crash - only that afterward, he had grabbed his bag, left the battered engine car, and dialed 911 on his cellphone, sources said.

That would be his last conversation with police, sources said.

The tracks leading in and out of 30th Street Station would have been familiar territory to Bostian, said an Amtrak conductor who worked with him regularly over the last four years.

"When he's in training, that is the route he would train on," said the conductor, who requested anonymity because of concerns about reprisals from Amtrak. "He would have an intimate knowledge of it."

The conductor described Bostian as friendly during down time but professional while manning a locomotive.

"He was always very pleasant, eager to do the job and learn," the conductor said.

Bostian had been working around trains since 2005, according to his LinkedIn page. That year, he began working for Amtrak as a passenger conductor, a position he held until 2010. At the end of that year he changed positions to become an engineer, the train's operator.

People in the rail business were riled by comments from Nutter that they interpreted as blaming the derailment on Bostian.

"He's already been pinned as the scapegoat," said Paul Pokrowka, legislative director for the Sheet Metal, Air, Rail and Transportation Union, and, for 15 years, an engineer on freight trains. "Mayor Nutter called this man reckless before we had any facts."

Bostian, who grew up in the Memphis suburb of Bartlett, attended the College of Business at the University of Missouri-Columbia, and lived in Queens. At his apartment building there, reporters and photographers clustered on Thursday afternoon. His building supervisor described him as "always polite."

On Bostian's Facebook page, more than 70 comments posted since Wednesday were universally supportive and suggested a man with a strong social network.

"You lived and breathed trains and didn't care," posted one friend, Jeffrey Betro.

Betro described Bostian hanging around train stations and riding trains for the joy of it. "You're a wonderful person, and it's hard to imagine what you're going through right now, but you're very clearly not alone," wrote Cole Bradley.

A regular commenter on the forum identified himself in two posts as "Brandon Bostian" and, over 12 years of posts, appeared to be a stickler for the rules.

He wrote as a knowledgeable train enthusiast who criticized railroad officials for not adopting certain safety measures over the years, expressing fluency with the complex rules that govern rail operations, and a sense of responsibility for his passengers. In one 2008 post, he chastised both a crew that tried to cover up a near-collision and the railroad for putting blame solely on the crew.

"Instead of looking at ways to prevent incidents like this, the solution is oftentimes to throw the book at crews and pretend that is a solution to the problem," he wrote.

Several times, he commented on what he perceived as railroads' failure to implement even "common-sense" safety measures.

"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 poster wrote.

215-854-2759 @MikeNewall

Inquirer staff writers Angelo Fichera and Ben Finley contributed to this article.