​What the NTSB will investigate in Amtrak derailment

The National Transportation Safety Board says it will be focusing on why Amtrak Train 188 was traveling at 106 mph before it derailed near Philadelphia, killing seven and injuring more than 200.

NTSB board member Robert Sumwalt CBS News

Robert Sumwalt, the NTSB's lead investigator in the probe, told CBS News the agency will look at the track, the traffic control signals, and the train's mechanical condition.

"Nothing is off the table, everything is on the table right now," said Sumwalt.

In an interview with "CBS Evening News" anchor Scott Pelley, Sumwalt said the NTSB plans to interview the engineer of the train who has been identified as Brandon Bostian.

Watch the video above to hear Sumwalt explain the next steps in the NTSB's investigation.