"For somebody to reach a point where they lose control, it takes a series of problems that build over time," said Robbins. "The person is usually not good at managing his or her anger."
There are also like to be other psychological issues at play.
"For someone to do something like this, there are gross distortions in their thinking. They are pretty disconnected from reality," said Ragan.
Ragan added that it's hard to determine exactly what those issues are, making it hard to predict whether a person may be prone to this sort of extreme violence.
"We don't have first-hand experience doing psychological post-mortem, and there are too many factors that are biological and psychological."
He cited two spree killers in particular who were believed to be biologically or psychologically impaired. Charles Whitman, who fatally shot 14 people and wounded 32 others at the University of Texas at Austin in 1966 was found to have a malignant brain tumor. Seung-Hui Cho, who killed 32 people and wounded numerous others at the Virginia Tech in 2007 had been diagnosed as mentally ill. While these men did not lash out where they worked, they fit the mold of spree killers who do.
Even if the beer distributorship or the union did address Thornton's allegations of racism, that doesn't mean it could have prevented him from snapping.
"There are people at workplaces that aren't interested in talking about their feelings, and these people are most often at-risk for violence," said Robbins.
"Unless there was evidence that he was telegraphing his intentions, there was no way to predict this would happen," said Ragan. "The workplace may have been an innocent bystander."