Sumwalt said that while the findings were "preliminary," he was confident that the 106 m.p.h. figure was within "1 or 2" m.p.h. of the actual speed. The curve was not equipped with a safety device that might have prevented the mishap.
The derailment occurred at 9:21 p.m., 11 minutes after the New York-bound train had left 30th Street Station. As investigators examined the wreckage late Wednesday, the silver cars, one of them "twisted like an aluminum can," lay in a zig-zag pattern.
"It is clearly, at a minimum, irresponsible to have a train going so fast," Nutter said.
Law-enforcement officials identified the engineer as Brandon Bostian, 32, of Forest Hills, N.Y.
The medical examiner was in the process of contacting the families of the dead, and the search for more bodies was continuing, Mayor Nutter said at a midafternoon briefing at the site.
More than 200 people were injured, and at least eight people remained in critical condition.
Nutter said President Obama had contacted him to pledge the federal government's "full support." In a statement, the President commended the first responders and medical personnel as well as uninjured passengers who assisted the injured.
"Along the Northeast Corridor, Amtrak is a way of life for many," he said. "From Washington, D.C., and Philadelphia to New York City and Boston, this is a tragedy that touches us all"
The incident marked the deadliest crash on the Northeast Corridor since 16 people were killed when an Amtrak train collided with a pair of Conrail engines near Baltimore in 1987.
Sumwalt said that investigators would be looking at "perishable evidence" at the scene but that it would be some time before NTSB drew conclusions. Mayor Nutter said the train's event recorders had been recovered and were being examined at an Amtrak facility in Delaware.
The curve at Frankford Junction is not yet equipped with a system called Positive Train Control that would automatically slow a speeding train.
Sumwalt said the train also was equipped with a forward looking video camera and that would be part of the investigation.
Bostian and the conductor survived the crash.
Bostian declined to give a statement to police investigators and left the East Detectives Division with an attorney, Police Commissioner Charles H. Ramsey said Wednesday.
The unidentified conductor was at Einstein Medical Center Philadelphia with a skull fracture, Ramsey said.
Thousands of commuters in the meantime scrambled to find alternate ways to work as the derailment has halted Amtrak service between New York and Philadelphia as well as service on SEPTA's Trenton line. SEPTA said the Trenton line could remain out of operation for the remainder of the workweek.
Amtrak Train 188, was bound to New York from Washington with 238 passengers and five crew members aboard.
In the moments after the derailment, scores of emergency personnel swarmed over the toppled train cars, trying to reach the dazed, the injured, the dying.
"Our first responders saved lives," Nutter said. "It's almost equally miraculous that 200-plus people -- that they were able to come out of that."
Surveying the wreckage from a hill, Philadelphia Police Officer Damien Stevenson said one of the cars tilted was "twisted like an aluminum can." He saw papers fluttering from broken briefcases.
Some people were reported trapped in the train, and crews cut into the cars to free the injured.
One of the dead was identified as Associated Press employee James Gaines, 49, a father of two, who died at Temple University Hospital. He had attended meetings in Washington and was returning home to Plainsboro, N.J.
The U.S. Naval Academy said a midshipman on leave also was killed. His family identified him as Justin Zemser, a 20-year-old from Rockaway Beach in Queens, who was in his second year at the Academy. In a published statement, his parents said: "This tragedy has shocked us in the worst way and we wish to spend this time grieving with our close family and friends."
The family of Rachel Jacobs, the CEO of an online learning start-up based in Philadelphia, said she had died in the accident. And Wells Fargo confirmed that Abid Gilani, 55, a senior vice president based in New York City, died in the accident.
Among the seriously injured was Eli Kulp, a nationally prominent award-winning chef of the restaurants Fork, High Street on Market, and a.kitchen.
Maryland business executive Robert Gildersleeve, 45, was among the unaccounted-for, and members of his family traveled to Philadelphia to try to find information about him.
"We went to all the hospitals several times, and Bobby's brother has been on the scene for the last 15 hours," said his sister, Doreen DeMarco, 47, of Holmdel, N.J.
Gildersleeve's daughter, Ryan, 15, and his son, Marc13, distributed flyers bearing their father's picture outside the Marriott Downtown Hotel on Market Street, where the Red Cross had set up a center for families.
Herbert Cushing, Temple's chief medical officer, said the hospital had received a total of 54 patients, 22 of whom remained hospitalized Wednesday. He said most of the injured had suffered broken ribs and that "the rib fractures tell me that they rattled around in the train car a lot."
He said some of the victims were covered with gravel and dirt from being thrown from the car.
"The patients who were awake and could talk to me were folks that were in the last two cars," Cushing said.
Gaines's family said that he usually rode in the front car, behind the engine.
Cushing said patients described the crash scene as chaotic. "The folks I talked to were injured because people fell on them or things fell on them."
He said the patients included visitors from Spain, India, and Albania who "just happened to be here on that train."
Among the injured was Caleb Bonham, 28, who was treated at Aria Health's hospital, in Torresdale, and released.
He was in the last car of the train, listening to music on his iPod when he noticed that his computer started shaking. Suddenly "everything went black," he said.
"Next thing you know, you wake up and you're on the other side," he said. He was thrown to the opposite side of the train car.
Passengers' belongings were scattered all over, he said. Even the train seats had tumbled around the car.
"There was stuff flying all over the place."
He said he exited through a rear door and saw where two other train cars had buckled together and lifted off the ground; some passengers were walking underneath and taking photos.
To honor the victims of the derailment, Gov. Wolf ordered all Pennsylvania flags in the Capitol Complex in Harrisburg and at state offices throughout Pennsylvania facilities statewide to fly at half-staff until sundown Sunday.
Contributing to this story were Daily News staff writers Dana DiFilippo and Stephanie Farr and Inquirer staff writers Michael Boren, Ben Finley, Caitlin McCabe, Craig McCoy, Laura McCrystal, Mike Newall, Paul Nussbaum, Chris Palmer, Jessica Parks, Mike Vitez, Aubrey Whelan, and Martha Woodall.