(Bloomberg) -- The Amtrak engineer at the controls of aspeeding train that derailed in Philadelphia last year, killingeight people, was distracted in the moments before the accident,U.S. investigators are preparing to conclude at a meetingTuesday.

The NationalTransportation Safety Board’s staff is proposing that arock-throwing incident involving a separate commuter train, whichthe engineer knew about because it was discussed in radiobroadcasts, most likely led him to lose awareness of speed limits,two people briefed on the discussions said. They asked not to beidentified because they weren’t authorized to speak about thematter before the meeting.

In addition to the dead, more than 200 were injured when thetrain carrying 238 passengers derailed in a shower of sparks on May12, 2015, as it sped into a curve at speeds ashigh as 106 miles (171 kilometers) an hour, more than twice thelimit.

Another issue that will be discussed by the NTSB is technologyknown as Positive Train Control that would have prevented theaccident by automatically limiting the train’s speed, the peoplesaid. Since the accident, Amtrak completed installing PTC on railsit controls in the corridor between Washington and Boston.

Board debating

Board members at the NTSB, who have final say on what the reportwill conclude, were still debating some of the issues, the twopeople said. They could alter the staff’s recommended findings andchange the emphasis somewhat, they said.

Evidence at the scene and a black-box recorder on the train havegiven investigators a clear picture of how the train was operatedand allowed them to rule out such things as mechanical failures.But there is scant evidence of what was going on inengineer Brandon Bostian’s head.

Bostian, 31 at the time of the accident, was in goodhealth, hadn’t been distracted by a mobile phone and testednegative for drugs, according to investigators. After being hit onthe head in the collision, he doesn’t remember what happened in themoments before impact, he told the NTSB.

At controls

“I remember turning on the bell, and the next thing that I rememberis when I came to my senses I was standing up in the locomotive cabafter the accident,” he told investigators a year ago.

Bostian was at the controls when the train sped up, suggestingthat he commanded the increase.

The stretch of tracks just beyond the curve had a speed limit of110 miles an hour.

Even without a clear idea of what led Bostian to speed up, theaccident will allow the NTSB to push for automated technology thatcould prevent such mishaps in the future and to emphasize the needfor transportation workers to avoid distractions.

Related: Amtrak sued by train crash victims over deadlyderailment

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