All of the locomotives' controls could only be manipulated manually by the engineer when it derailed. The engine was not aging equipment as it was only a year old and had no reported history of unintended acceleration. Bostian was not talking on the phone, texting or using smartphone data during the accident, nor was he using alcohol or drugs. The NTSB has told Congress that human error is a likely factor. Bostian's lawyer said that his client does not recall much about the accident because of a concussion he sustained in the wreck, but that "he remembers coming into curve. He remembers attempting to reduce speed and thereafter he was knocked out." The NTSB interviewed Bostian on May 15, who said he had "no recollection" of events after the train passed North Philadelphia station. Lead NTSB investigator Robert Sumwalt said Bostian was "extremely cooperative". Earlier, Sumwalt had said, "for somebody who's been through a traumatic event, this is not at all unusual for human behavior to have the mind blank out things like that, at least for the short term." According to "The New York Times Magazine", investigators focused on two possibilities: that a rock hit the windshield of the locomotive and caused Bostian to be distracted or disoriented, or that he mistakenly believed he was in a different curve. Both would result in Bostian losing situational awareness and allowing the train to enter the curve too fast. At a hearing on May 17, 2016, the National Transportation Safety Board reported that the primary cause of the derailment was a loss of situational awareness by the train's operator, likely caused by distracting radio chatter from a nearby SEPTA train that had experienced an emergency situation. Somebody had thrown a rock at the SEPTA train's windshield, causing it to shatter and blind the conductor. This distraction resulted in the operator believing he was further down the track than he was, thus accelerating the train before the curve rather than after it. The board concluded that the accident would have been entirely prevented if the line was equipped with positive train control, which would have recognized and applied the appropriate speed limit, and chairman Christopher A. Hart called on federal railroad regulators to "end this list of PTC preventable fatalities and injuries right now." Philadelphia Mayor Michael Nutter said of the wreck, "It is an absolute disastrous mess." Pennsylvania Governor Tom Wolf said, "Anything that the state can do, we stand ready to do that." Amtrak was "deeply saddened by the loss of life from Amtrak Northeast Regional Train 188," according to a statement released on May 13.