PHILADELPHIA—A jury cleared an Amtrak engineer Friday of all charges stemming from a derailment that left eight people dead and hundreds injured in Philadelphia in 2015, concluding that his operation of the train at more than twice the speed limit on a curve didn’t constitute criminal negligence. The jury took just over an hour to acquit Brandon Bostian, 38, of causing a catastrophe, involuntary manslaughter and reckless endangerment—one count for each injury and death. Amtrak had earlier settled civil litigation over the crash for $265 million. The train rounded a curve at about 106 mph, more than twice the 50 mph speed limit, before it derailed in north Philadelphia. Bostian’s lawyer described him as a lifelong train buff who had a perfect work record until he was distracted by reports of people throwing rocks in the area just before the crash. He could have been sent to prison for years, …