Friday's accident marks the second train derailment at the freight-only bridge over the Mantua creek since 2009.
The NTSB says it was not involved with the previous accident, but it is heavily involved now.
NTSB chairwoman Deborah Hersman says their independent agency has never investigated accidents at the site, but now they are requesting several documents dating back to before the 2009 derailment to get to the bottom of Friday's accident.
"We are looking at these records prior to that event in 2009. We are looking at what work was done, when the bridge was repaired and after, and we are looking very closely at inspection records associated with the bridge over the creek," said Hersman.
Officials on scene were not aware of any accidents prior to 2009, but say that Conrail, who owns and operates the movable bridge, invested in extensive repairs to the structure in 2010.
John Burzichelli says the bridge was built in the early 1900s.
It is unclear when it was last inspected, but residents reported seeing Conrail representatives at the site just a couple of days ago after people say they heard a loud, uncharacteristic bang on the swing bridge.
"Whatever they observed apparently didn't stand out enough to say the bridge was not safe to cross," said Burzichelli.
No passenger trains travel over the bridge, only freight trains.
The NTSB investigation will try to determine whether the derailment was caused by a problem with the bridge or if the derailment was to blame for the bridge's partial collapse.