DUPONT, Wash. — The investigation into the fatal Amtrak crash near Tacoma, Wash., is focusing on the possibility that the engineer was distracted by a cellphone, another person in his cab or something else when the train barreled into a curve 50 miles per hour over the posted speed limit.

The crew did not activate the emergency brake before the derailment on Monday morning, said Bella Dinh-Zarr, the National Transportation Safety Board official overseeing the investigation, which might indicate that the engineer failed to perceive the danger.

At a news conference on Tuesday afternoon, she said the badly damaged cameras in the engineer’s cab — one facing forward, and the other inward, toward the person driving the train — had been sent to the safety board’s laboratory in Washington D.C. There, investigators will try to extract images showing what went on in the moments before the train plunged into a stand of trees and onto a busy highway, killing three people.

Ms. Dinh-Zarr stressed that the crew members — all of them hospitalized — had not yet been interviewed, and most of the evidence not yet analyzed. A data recorder on the train, carrying 77 passengers and seven crew members, indicated that it was racing at 80 miles per hour into a curve that is limited to 30 miles per hour, the safety board said. Excessive speed appeared to be the immediate cause of the crash, but the reason for that speed remained unknown.

“Distraction is one of our most wanted list of priorities at the N.T.S.B.” she said. “It’s protocol for us to look at all of the cellphone records of all the crew members whenever there is an accident of this type.”

There was a second person in the cab at the time of the crash, “a conductor who was getting experience and familiarizing himself with the territory,” Ms. Dinh-Zarr said. While that is common practice, rail safety experts say it can also be a distraction to the engineer, a possibility that she said would be investigated.

Drug and alcohol testing of crews is routine after train accidents, and the inward-facing cameras could show not only whether the engineer was distracted, but also whether he was impaired or fatigued — factors that have been blamed in other rail accidents.