(CNN) - The crew on the passenger train that derailed this week in Washington state was not seen using any personal electronic devices, an initial review from the National Transportation Safety Board said Friday.
The Amtrak Cascades train 501 derailed Monday near DuPont, Washington, and hurtled off an overpass onto Interstate 5, killing three people and injuring dozens more. The train was on its inaugural journey from Seattle to Portland, Oregon.
The NTSB review said the "lead locomotive's event data and video recorders were successfully downloaded with the manufacturer's assistance and processed" in Washington at the NTSB laboratory.
The review noted that "inward-facing video with audio captured the crew's actions and their conversations. A forward-facing video with audio captured conditions in front of the locomotive as well as external sounds."
The review made these other points:
• The engineer "made a comment regarding an over speed condition" about six seconds before the derailment.
• Video shows the engineer applied the brakes, but it does not appear he placed the brake handle in emergency-braking mode.
• The video recording ends as the locomotive was tilting and the crew was bracing for impact.
• The train's final speed was 78 mph.
The investigation is expected to last anywhere from a year to two years, the NTSB said.
"A preliminary report detailing the facts and circumstances of the crash developed in this early stage of the investigation will be available on the NTSB website in the coming days," the agency said.
It's unclear why the train was traveling at a high speed in a 30-mph zone. Adding to the mystery, technology called positive train control, or PTC, which can automatically slow down a speeding train, wasn't activated.
"The locomotive was in the process of getting a system of PTC installed, but it was not yet functional," NTSB member Bella Dinh-Zarr said.
The NTSB has recommended the use of PTC for decades. Railroad companies have until the end of 2018 and a possible extension to 2020 to implement the costly system.
A Chicago law firm has been hired to represent six people injured in the derailment, according to Michael Krzak, an attorney with Clifford Law Offices. They suffered physical injuries and potential long-term emotional damage, Krzak said. The firm has not filed any lawsuits so far.