Accident investigators said Wednesday that the engineer driving an Amtrak train wasn't using his cellphone in the moments before the train derailed in Philadelphia last month, deepening the mystery of what caused the accident.

Eight people were killed and about 200 more injured in the May 12 derailment.

In an updated report, the National Transportation Safety Board said its analysis of phone records "does not indicate that any calls, texts or data usage occurred during the time the engineer was operating the train."

The agency also said the engineer, Brandon Bostian, didn't access the train's Wi-Fi system while he was operating the locomotive.