Prosecutors say the engineer who fell asleep at the controls of a commuter train that derailed in New York City in 2013, killing four people, won't face criminal charges.

A spokeswoman said Thursday that Bronx District Attorney Robert Johnson found no criminality in the December 2013 Metro-North Railroad derailment.

The National Transportation Safety Board says engineer William Rockefeller fell asleep at the controls because of undiagnosed sleep apnea combined with a drastic shift in his work schedule. It says that caused him to take a 30 mph curve at 82 mph.

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