-- The slaying of two journalists on live television Wednesday became more shocking when the suspected gunman posted video he says he took of the shooting to his Facebook page, delivered a 23-page document about his motives and tweeted after the attack.
By poring over the documents believed to have been sent by Vester Flanagan, one expert said, there may be some lessons to help prevent similar events in the future.
"We can then study it and analyze it by terms of dominant themes that predicted what he did," Frank Farely, a professor at Temple University in Philadelphia and former president of the American Psychological Association, who has not seen the document. "It’s a terrible, terrible tragedy, but the tiny little itsy-bitsy silver lining is that it will help science provide some help in ... prevention."
In the document faxed to ABC News less than two hours after the shooting, Flanagan lays out multiple grievances and talks about how shootings at a predominantly black church in Charleston, South Carolina, this year was a "tipping point” for him.
Farely explained that few people make their motives so clear before going on similar revenge or mass killings. By looking at past warning signs or indications of Flanagan's state of mind in the months or weeks before his alleged actions, Farely said, experts may be able to identify worrisome signs in patients and take action.
"It’s the kind of case study you want the graduate class to work on to get at motive," he said.
Peter Langman, a psychiatrist in Allenton, Pennsylvania, and an expert on school shootings, said the profiles of people who commit mass shootings or revenge killings often include people who are narcissistic or psychopathic and take rejection personally.
"If they get disciplined and get fired, it’s an injustice and they’re the victim," Langman said, explaining it's possible that in Flanagan’s mind “he was being done wrong over and over again.”
Additionally, he said, some shooters exhibit signs of psychosis where they have delusions or become paranoid that someone or something has turned against them.
"You see the same dynamic in that people are out to get them; it’s based in their own paranoia," Langman said.
He also dismissed the likelihood that Flanagan simply "snapped" before the alleged shooting.
In the faxed document, Flanagan cited the Charleston attack, writing: "The church shooting was the tipping point… but my anger has been building steadily ... I’ve been a human powder keg for a while…just waiting to go BOOM!!!!"
But Langman said the idea of "snapping" for revenge or mass shooters is uncommon and that it appears from the letter there was a long history of anger that allegedly led him to take violent action.
"There’s something that was building for a period of time," Langman said of mass killings in general. "When you’re talking about planned large-scale attacks … no one thing contributes to it."
Langman explained that there are often warning signs before a violent event, usually as the killer plans the attack as they might “leak” something to friends or family. There is no indication at this point that Flanagan did that.