Officials survey the site of a derailed Amtrak train in Philadelphia, PennsylvaniaBy Daniel Kelley PHILADELPHIA (Reuters) – Rescue workers on Wednesday sifted through twisted metal and other debris from the wreck of an Amtrak train that derailed in Philadelphia, killing at least six people and injuring scores of others, while investigators reviewed data to determine the cause of an accident. Philadelphia Mayor Michael Nutter said authorities had not yet accounted for everyone aboard the train. Officials of the National Transportation Safety Board had recovered recorders, or black boxes, from the train and were analyzing data, Robert Sumwalt, a NTSB member, said at the news conference. The crash of Amtrak train No. 188, en route from Washington, D.C. with a crew of five, was the latest in a series of rail accidents on heavily traveled passenger train routes over the past year.