A spokeswoman for the National Transportation Safety Board said a switch was in the wrong position at a train wreck in Aiken County Thursday that killed nine people.

The victims died from chlorine vapors after a tanker car ruptured in the wreck involving a moving freight train routed onto a siding at a textile mill, where it hit a parked train.

NTSB spokesperson Debbie Hersman says the crew of the parked train should have left the switch aligned with the main line. She said it doesn't appear that was done.

Hersman said investigators are examining how that happened. She said the crew is being interviewed and officials are back tracking on what the crew had done in the previous 96 hours.

Hersman says officials are reviewing dispatch and inspection records.

Crews placed a temporary patch on the ruptured car over the weekend.

Officials said they will try to patch the car and unload the remaining chlorine gas Monday.