Was a tragic derailment a “terrible accident” or did the train engineer recklessly fail to do his job at a dangerous point in his route?

On Friday morning, prosecutors and defense attorneys laid out opposing perspectives on the line between an accident and a crime in the case of Brandon Bostian, the train engineer onboard when Amtrak train No. 188 derailed in Philadelphia in 2015.

Both sides agree on the facts of the derailment itself. Bostian’s train departed 30th Street Station shortly after 9 p.m on May 12. It picked up speed as it headed into a tight curve near Frankford Junction, reaching 106 mph when the speed limit was 50 mph. Bostian braked, but the train derailed seconds later, killing 8 people and sending