INSIDE THE AMTRAK TRAIN CRASH

May 13: Emergency personnel walk near the scene of a deadly train wreck in Philadelphia. An Amtrak train headed to New York City derailed and crashed in Philadelphia on Tuesday night. (AP)

May 12: Emergency personnel work the scene of a train wreck in Philadelphia.  (AP Photo/Joseph Kaczmarek)

May 12: A crime scene investigator looks inside a train car after a train wreck in Philadelphia.  (AP Photo/Joseph Kaczmarek)

May 12: Emergency personnel work the scene of a deadly train wreck. (AP Photo/ Joseph Kaczmarek)

May 12: Emergency personnel work the scene of a deadly train wreck in Philadelphia.  (AP Photo/ Joseph Kaczmarek)

May 12: Emergency personnel work the scene of a deadly train wreck.  (AP Photo/ Joseph Kaczmarek)

May 12: Emergency personnel work the scene of a train wreck. (AP Photo/Joseph Kaczmarek)

May 12: Emergency personnel work the scene of a deadly train wreck. (AP Photo/ Joseph Kaczmarek)

As many as six more people remain critically injured, some were unaccounted for and more than 140 more riders were being evaluated and treated at local hospitals, as federal investigators were on scene to determine what caused the accident. (AP Photo/ Joseph Kaczmarek)

Amtrak and city authorities estimated that 238 passengers and five Amtrak employees were on the Northeast Regional Train 188, traveling from Washington, D.C., to New York City, when it went off the rails at about 9:30 p.m. local time. (AP Photo/ Joseph Kaczmarek)

May 13: A worker passes one of the cars of a derailed Amtrak train. An Amtrak passenger train with more than 200 passengers on board derailed in north Philadelphia on Tuesday night, killing at least six and injuring more than 50 others, several of them critically, authorities said. (Reuters)

May 12: Emergency personnel help a passenger at the scene of a train wreck. (AP Photo/Joseph Kaczmarek)