NEW YORK » No criminal charges will be brought against the engineer who fell asleep at the controls of a New York City commuter train in 2013, leading to a derailment that killed four people, prosecutors said Thursday.

The National Transportation Safety Board concluded last year that the Metro-North Railroad engineer, William Rockefeller, nodded off because he suffered from an undiagnosed sleep disorder and had a drastic shift in his work schedule.

"There was no criminality in the act, therefore no criminal charges," said Terry Raskyn, spokeswoman for Bronx District Attorney Robert Johnson. She said Johnson had decided several months ago not to bring charges.

The decision was made public in the midst of an investigation into a similar railway accident, the derailment of an Amtrak train in Philadelphia that killed eight people this week.

Rockefeller’s lawyer, Jeffrey Chartier, said the district attorney "came to the only logical conclusion, which is the same as the NTSB — which is that there’s no criminality on the part of Mr. Rockefeller. It was simply a tragic accident."

He said Rockefeller is struggling with post-traumatic stress stemming from the crash and is unable to work.

"It’s something that haunts him every day, and I’m hoping the public acknowledgement that he didn’t do anything wrong will be some healing and closure for him," Chartier said. "His heart is still broken for all those people who were affected by this."

The dead were Kisook Ahn, a nurse returning home to New York City from an overnight shift in Ossining; Jim Lovell, a "Today" show lighting technician on his way to work on the Rockefeller Center Christmas tree; Donna Smith, a paralegal heading into the city to hear her sister sing Handel’s "Messiah" with a choral group; and James Ferrari, a building maintenance worker putting his daughter through college.

Calls to several survivors of the victims were not immediately returned.

In the crash Dec. 1, 2013, Rockefeller’s train was headed for Grand Central Terminal from Poughkeepsie when itderailed as it hit a curve in the Bronx at 82 mph, the federal investigators said. The speed limit on the turn was 30 mph. In addition to the four people killed, more than 70 were injured.

Rockefeller told investigators that right before the crash, "it was sort of like I was dazed, you know, looking straight ahead, almost like mesmerized." He said he was roused only when he sensed "something wasn’t right" with the train and threw on the emergency brake.

After testing, the NTSB concluded he had undiagnosed sleep apnea, which robs its victims of rest because they are repeatedly awakened as their airway closes and their breathing stops. The NTSB said Rockefeller’s apnea interrupted his sleep dozens of times each night.

The board recommended better screening for sleep disorders in engineers.

Chartier said New York allows for charging someone who knowingly or recklessly disregards a risk or fails to perceive one when a reasonable person would. But "none of that existed in this case" because Rockefeller didn’t know of his condition, Chartier said. "He couldn’t be held responsible for something he had no knowledge of."

Meanwhile, investigators are trying to determine why the Amtrak train that crashed in Philadelphia on Tuesday night was careering through the city at 106 mph before it ran off the rails.

Associated Press Writer Jim Fitzgerald in White Plains, New York, contributed to this report.