There's someone out there who threw the rock.

On May 12, 2015 someone threw a projectile that hit a SEPTA train. Officials are now saying that act may have set in motion a hideous Rube Goldberg-like chain of cause and effect that permanently altered life for hundreds and ended it for eight.

The object, probably a rock, shattered the train's windshield, throwing glass in the engineer's face, and forced him to stop the train.

According to Tuesday's National Transportation Safety Board Investigation, the impact spurred a flurry of radio chatter about what happened, where the train was and if the engineer was alright.

Listening in was Brandon Bostian, operator of Amtrak train 188 heading on the northbound tracks on a course that would bring it right past the area where the SEPTA train was struck just minutes after the rock throwing incident. Bostian, described as a conscientious engineer by investigators, was concerned. He was worried about the engineer of the other train. He had a friend who had been operating a vehicle struck by a rock, and knew how ugly injuries could be. He was worried that maintenance workers tending to the damaged train could end up being in the path of his own.

The radio chatter was so distracting, the NTSB concluded Tuesday, it may have been the thing that broke Bostian's concentration on his own duties and caused him to accelerate into a turn at more than double the posted speed. His train derailed.

It may have all happened because someone threw a rock. That person has never been found.

"That night we did not catch the guy," said SEPTA Police Chief Thomas Nestel III. "The train engineer didn't see where the rock came from or who threw it. He stopped shortly after getting struck. We sent people up to search the track area but didn't find anything."

It's not that unusual. Another train, an Acela, was hit earlier the same night in the same general area. There had been six other stone throwing incidents reported within five miles of the derailment site since 2012, according to the NTSB investigation, and Nestel noted these things are usually only reported if a rock hits a train head on. Under normal circumstances, rock throwing isn't even treated like a big deal, he said.

"Most of the time, we have cameras on the trains, and we track down some of the kids," Nestel told her. "This is one of those issues that we generally leave to parents and schools to adjust."

So who knows if that person has been following the news or if the person feels remorse over maybe playing a role in ruining lives. Much of today was spent deciding the reasons why eight people are dead. There's responsibility to go around, but for every other cause cited there's a person or agency who we can identity to take responsibility.

Except for one person who threw a rock.