Sumwalt convened the briefing several hours after the body of the eighth - and final - victim of the Frankford Junction Amtrak derailment was found trapped inside wreckage at the crash site, officials said.
Mayor Nutter made the announcement as the National Transporation Safety Board was wrapping up its work at the scene, with Police Chief Inspector Joseph Sullivan calling the search for the cause an "ongoing, active criminal investigation."
Nutter implored Bostian to tell officials whatever he could recall. "The 243 people on that train, and certainly the families of the eight who died, they deserve answers," he said.
The tragic incident has disrupted service for commuters along Amtrak's busiest rail corridor, used by millions annually, and has affected two other lines.
Mayor Nutter said officials now believe that all 243 people who were on Amtrak Train 188 have been accounted for.
More than 200 people were injured, about 150 were taken to seven area hospitals, and and six remained in critical condition late Thursday.
Five people were known to have died the night of the derailment, a sixth the next day - Wednesday - at Temple University Hospital, and a seventh victim was found at the site, also on Wednesday.
Fire Commissioner Derrick Sawyer said the eighth victim was found in the wreckage of the mangled first passenger car with the aid of a cadaver dog about 8 a.m. Thursday. Firefighters had to extract the remains from the twisted steel, Sawyer said.
All eight have been identified through various sources as Laura Finamore, 47, a corporate real estate officer, Derrick Griffith, 42, a dean at Medgar Evers College, and Rachel Jacobs, 39, an online startup executive, all of New York City; Jim Gaines, 48, an Associated Press employee, of Plainsboro, N.J.; Abid Gilani, 55, a bank executive, Rockville, Md.; Bob Gildersleeve, 45, an Ecolab executive, Elkridge, Md.; Giusseppe Piras, 41, an olive-oil and wine merchant, Sardinia, Italy, and Justin Zemser, 20, U.S. Naval Academy midshipman from Queens, N.Y..
Sumwalt said earlier all but two of the damaged passengers cars have been removed from the scene and that his team of investigators will conduct 3D scans of the two remaining cars, which were the most seriously damaged.
The closure at Franklin Junction not only has halted Amtrak service between New York and Philadelphia and, by extension, New York and Washington, it has forced 12,000 daily riders who use SEPTA's Trenton Line to find alternate routes to work, and has prevented NJ Transit's Atlantic City line trains from getting to and from 30th Street Station. About 1,200 riders use that service daily.
Joseph Boardman, Amtrak's chairman said limited to full service is expected by Monday morning.
Amtrak officials were "heartbroken" for the families of the victims, Boardman said in an interview.
But noting that this was Amtrak's first fatal derailment in 28 years, Boardman said, "This is a damn safe railroad."
Boardman defended the decision not to install "positive train control," or PTC system, at the curve. Officials have said the derailment could have been prevented if a PTC system, which would have braked the train automatically, was in place at the junction.
Boardman said the agency has been underfunded and needed additional equipment for the system to work.
U.S. Rep. Robert A. Brady (D., Pa.) called for the Federal Railroad Administration to publicly release all documents relating to the implementation of PTC, mandated by Congress in 2008.
"This week's tragedy in Philadelphia was not caused by a failure of technology," Brady said in a statement, "it was a failure of political will to implement the technology we have that could have avoided the loss of lives."
Daily News staff writer Dana DiFilippo and Inquirer staff writers Michael Boren, Melanie Burney, Caitlin McCabe, Laura McCrystal, Justine McDaniel, Mike Newall, Paul Nussbaum, and Aubrey Whelan contributed to this article.