Prosecutors in Philadelphia will not press charges against an Amtrak engineer who was operating a train when it derailed in Pennsylvania in 2015, killing eight people and injuring 200 others.

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The Philadelphia District Attorney's Office said Tuesday that there was no evidence that engineer Brandon Bostian acted with "conscious disregard" when he sped up on the Franklin Junction curve on May 12, 2015.

However, authorities said, “The evidence indicates that the derailment was caused by the engineer operating the train far in excess of the speed limit.”

Bostian was traveling at 106 mph on a 50 mph curve when the train derailed. Federal investigators concluded that Bostian lost track of his location before the crash, after learning a nearby commuter train had been struck with a rock.

Investigators did not find any evidence of drugs or alcohol in Bostian’s system or find evidence he was distracted by a cellphone or other device.

Victims' lawyers Tom Kline and Robert Mongeluzzi described their clients as bitterly disappointed and said many remain in constant pain two years later.

"There are people in relentless, debilitating, brutal pain, who have lost their jobs, and who have lost their futures, because of Mr. Bostian's actions," Kline told The Philadelphia Inquirer last week. "I think it becomes even more important to hold people like him responsible."

The Associated Press contributed to this report.