Sources say engineer Brandon Bostian was distracted by radio traffic about a rock throwing incident involving a SEPTA train.
Sources say, according to the NTSB's findings, Bostian was worried because a friend had lost partial eyesight in a rock throwing incident.
That incident happened shortly before the derailment in North Philadelphia, about four miles from the Port Richmond crash scene.
Action News learned Monday night there was more to blame than just alleged human error.
A government official briefed on the NTSB's report says investigators believe there were issues with the train's emergency windows.
Of the eight people who died, some of them had been killed because they were ejected through those windows.
NTSB officials are scheduled to hold a board meeting in Washington on Tuesday where they will formally announce a probable cause of the crash.
The NTSB is also expected to make recommendations.
The New York-bound Northeast Regional train entered the sharp Frankford Junction curve at 106 mph, more than twice the speed limit, on the night of May 12, 2015, and tumbled off the tracks.
According to a previously released transcript of his interview with federal accident investigators, Bostian said the last thing he remembers is pushing the throttle forward to pick up speed and then braking when he felt the train going too fast into a sharp curve.
When he realized the train was about to derail, Bostian said he was holding tightly to the controls and thinking, "Well, this is it, I'm going over."
Sources say the NTSB found that Bostian may have thought he'd already passed the curve when he sped up.
The train's data recorder shows that at about 55 seconds - a mile and a half before the Frankford Junction curve, one of the sharpest in Amtrak's Northeast Corridor, Bostian applied full throttle and held it there for about 30 seconds. The train reached a speed of about 95 mph.
He then slightly lowered the throttle for 2 seconds before returning to full throttle and holding it there for another 20 seconds. Three seconds before the train derailed, at a speed of 106 mph, Bostian applied the emergency brake.
That reduced the speed to 102 mph, but by then it was too late. Four of the train's seven cars and its locomotive derailed in a tangled heap.
Bostian provided his cellphone to investigators, who say there's no indication he was using it while operating the train.
Other avenues of investigation have also turned up dry holes, according to previous statements by investigators. The data recorder shows the train's top-of-the-line new Siemens engine was functioning normally. No anomalies were found in the tracks or signal boxes. There was no vehicle or object on the tracks. Toxicology tests of Bostian found no drugs or alcohol.