jumped the tracks, plummeting on to the highway and vehicles below. >> we'll be we hope interviewing the crew to find out if they have more information that can help us figure this out. >> reporter: besides looking at whether a mechanical malfunction played a role, investigators are now focused on the crew controlling the train and whether human error caused the deadly derailment. >> it was like being inside an exploding bomb. >> there was this body lying there, i mean, it was -- he had -- hardly had any clothes on. the cloekts had just been ripped off him and he was obviously dead. >> reporter: while investigators have not determined the cause, amtrak's ceo says positive train control was not activated when the derailment happened. ptc is a technology which automatically slows down and eventually stops a train if it senses it's going too fast. sound transit, the company that owns the tracks, says the technology will be fully implemented by next spring. one of ntsb's board members