DUPONT, Wash. (AP) — Federal investigators probing a deadly Amtrak derailment are trying to determine why the train was traveling at more than double the posted speed limit as it entered the curve where it left the tracks and plunged off an overpass and partly onto a busy freeway, killing three people and injuring dozens.

Early details from the probe indicate a conductor-in-training was in the cab with the engineer at the time of the derailment and the brake that eventually stopped the train was automatically activated instead of being applied by the engineer, National Transportation Safety Board member Bella Dinh-Zarr said Tuesday.

A federal official told The Associated Press that investigators are looking into whether the engineer was distracted by the presence of an employee-in-training next to him in the locomotive. The official, who was not authorized to discuss the matter publicly and spoke on condition of anonymity, said investigators want to know whether the engineer lost “situational awareness.”

Investigators also confirmed that technology that can automatically slow or stop a speeding train — known as positive train control — was not in use on that stretch of track. Track sensors and other PTC components have been installed, but the system is not expected to be completed until the spring, Dinh-Zarr said. Regulators have been pressing railroads for years to install such technology, and some have done so, but the deadline has been extended repeatedly at the industry’s request and is now set for the end of 2018.

Dinh-Zarr said it was too early in the investigation to say whether positive train control would have prevented Monday’s tragedy but noted that a “mandate” to install the system on tracks nationwide by 2015 had been pushed back by Congress.

Sen. Richard Blumenthal, speaking on the floor of the U.S. Senate on Tuesday, said failing to enforce the new deadline to install positive train control would be a “moral failure.”

“If we do nothing else in this Congress, let us insist that deadline without additional delay,” said Blumenthal, D-Connecticut.

The train was hurtling at 80 mph in a 30 mph zone Monday morning when it ran off the rails along a curve south of Seattle, sending some of its cars plummeting onto an interstate highway below, Dinh-Zarr said, citing data from the locomotive’s event recorder.

Skid marks — so-called “witness marks” — from the train’s wheels show where it left the track, she added.

Federal investigators will remain on scene past Christmas to complete a wide-ranging investigation that involves at least eight local, state and federal agencies, rail lines and train car manufacturers.

The train, with 85 passengers and crew members, was making the inaugural run along a fast new bypass route that was created by refurbishing freight tracks alongside Interstate 5. The 15-mile, $180.7 million project was aimed at speeding up service by bypassing a route with a number of curves, single-track tunnels and freight traffic.

Investigators will talk to the engineer and other crew members and review the event data record from the lead locomotive as well as an identical device from the rear engine, which has already been studied.

Investigators are also trying to extract data from inward- and outward-facing onboard cameras that were damaged in the crash, Dinh-Zarr said.