The engineer at the helm of the Metro-North train that derailed on December 1st will likely not be charged, despite having admitted to "nodding off" as the train parted with the tracks, killing four and inuring more than 70 others.

Investigators have uncovered several key findings about train operator William Rockefeller's activities leading up to the tragic train derailment, DNAinfo reports: Sources say he went to sleep around 8:30 p.m. the night before, and that he wasn't distracted by his phone at the time of the crash. (It was turned off). There was no alcohol found in his system, and though toxicology tests have yet to produce results, sources assert that no preliminary evidence exists to suggest that Rockefeller was under the influence of any drugs.

“Falling asleep, by itself, is fundamentally not a crime, not even for a motorman driving a train,” one law enforcement official told DNAinfo.

Still, the National Transportation Safety Board confirmed that the train was traveling 82 mph when it entered the sharp turn in Spuyten Duyvil, well over the 30 mph recommended speed. Initially, Rockefeller blamed the brakes for the incident, but the NTSB disagreed: “simply put...there is no indication that the brake systems were not functioning properly,” said board member Earl Weener.

The Federal Railroad Administration is slated to begin an in-depth examination of the crash today. The probe, called Operation Deep Dive, will span 60 days.