The allegations of racial harassment that Omar Thornton told his family about may have been what finally sent him over the edge and on his fatal rampage, according to mental health experts.
"A common association with workplace violence is a recent experience of humiliation," said Dr. Ken Robbins, clinical professor of psychiatry at the University of Wisconsin-Madison. "It sounds like there may have been some of that." Robbins didn't know Thornton and is only speculating on what could have triggered the gunman's rage.
"There's a question about hostility in the workplace, and that could definitely have played a role," said Dr. Paul Ragan, senior consulting psychiatrist in the department of psychiatry at Vanderbilt University Medical Center.
Thornton's family believes the union knew about the racial harassment, but the union says it didn't. If the union or the company did know about the alleged instances of racism, experts say they should have addressed it.
"If anybody talks about an experience where they've been humiliated and they have feelings about it, it needs to be taken seriously," said Robbins. "It's important that workplaces develop an atmosphere where people do feel able to talk about something that is troublesome."
The alleged racism was just one event that could have led up to Thornton lashing out at his colleagues. ABC News has learned that Thornton, the man behind the murder-suicide at the Connecticut beer distributorship, was offered the chance to resign his job as a driver or be fired. There's no official word about the reason behind his termination, but sources said he was caught on video stealing beer from his employer.
"Suicides and violence can increase in economic hard times," said Ragan.
The events that unfolded in Connecticut are an example of extreme workplace violence, something that happens more frequently than we think.
"We know that violence is the second leading cause of occupational death. It's not as uncommon as we would like it to be," said Robbins.
There have been well-publicized incidents of extreme workplace violence prior to the events that unfolded in Connecticut, including the shootings of six employees, three fatally, at the University of Alabama's Huntsville campus in February and the shootings of 45 people, 13 fatally, at the U.S. Army base in Fort Hood, Texas in November.
While the true motives behind these events may be unclear and the alleged perpetrators very different, spree killers who seem to lash out at people in their workplace generally have certain psychological characteristics in common.
"The workplace is often a source of disappointment, and is the unfortunate recipient of the person's rage," said Dr. Ragan.
"People who have been violent often say they weren't aware they were becoming so angry. They say they felt as if they were going from zero to 100 and weren't aware of their anger earlier," said Robbins.
In most cases, it's not just one incident that causes spree killers to snap.