Mass shootings: Why it's so hard to predict who will snap

James Holmes sat subdued in court at his first appearance, declining to speak and looking dazed and confused. The appearance was short, and Holmes was silent as he was formally read his rights.

As the alleged shooter in last week's Aurora, Colo., movie theater killings made his first appearance in court, his every facial tic was scrutinized for clues as to why he might have launched his attack against theater-goers at a midnight showing of the newest Batman movie last week.

But even if James Holmes eventually reveals his motives, psychologists say, the answers are unlikely to be satisfactory.

"Even when you pull the pieces together, they really don't add up," said Mary Muscari, a forensic nurse at Binghamton University in New York who has researched mass killers. The histories of mass shooters sometimes show common threads, such as a series of disappointments leading up to the event, Muscari said. But in the end, the spark that drives people to violence is unknown, and the events are rare enough that it's hard to generalize from case to case.

"There are certainly a lot of people who have a lot of things go wrong, and they're not committing mass murders," Muscari told LiveScience. "Even when you look at mental illness, most people with mental illness are not violent."

Searching for a common thread

Holmes allegedly entered a theater showing the Batman film "The Dark Knight Rises" shortly after the movie began on July 20. Dressed in protective gear and bearing tear gas and three guns, Holmes opened fire on the crowd, killing 12. [10 Most Destructive Human Behaviors]

Mass killers follow different enough patterns that it's incredibly difficult for researchers to pin down common threads, said Frank Farley, a psychologist at Temple University and the past president of the American Psychological Association.

"Each one is a recipe with some common ingredients, perhaps, but then ingredients that differ," Farley told LiveScience. "For example, many are white males between 20 and 30. On the other hand, there are millions of such males in this country."

And there are exceptions to every trend. Seung-Hui Cho, who killed 32 during a shooting rampage at Virginia Tech in 2007, was of Korean descent. Eric Harris and Dylan Klebold, the perpetrators of the Columbine High School massacre in Littleton, Colo., were 18 and 17 years old, respectively. In a relatively rare case of a female perpetrator, University of Alabama, Huntsville professor Amy Bishop has been charged with killing three and injuring three more during a workplace shooting in 2010.

Mass killers can target strangers, coworkers or family members, Muscari said. A common motive is revenge, she added.

"Revenge is a fluid thing," Muscari said. "It could be something very specific against a certain person, it could be a general thing in the workplace or school, or it could be very diffuse, where they go shoot up a restaurant."

Mass killers are often portrayed as socially isolated loners, but that's not quite accurate, said Katherine Newman, a sociologist at Johns Hopkins University who has studied high-school and university shootings.

"In fact, they are very rarely loners," Newman said. "After the fact, when you interview people who knew them, they'll say, 'He had friends. I was one of his friends.' But in general, their social experience is not one of easy incorporation."

In other words, many mass shooters, rather than wanting to be alone, have a history of struggling to connect. They experience rejection by their peers or they draw back from potential friendships, assuming they'll be rejected if they try. They believe they're perceived as insignificant, Newman told LiveScience.

"They want to be seen as notorious, and unfortunately, there's a lot of social reinforcement for the glamour of being notorious," she said. "They imagine how cool it will be when everybody knows their name … I know this sounds absurd, but in some ways, revulsion or notoriety is preferable from their point of view from anonymous and insignificant." [10 Surprising Facts About the Teen Brain]

Extreme events

But even here, the psychology of mass killers remains evasive. Plenty of people struggle with friendships, Newman said, and only a "tiny, tiny infinitesimal fraction of them [does] something like this."

As soberingly frequent as mass shootings may seem, they're extremely rare from a scientific perspective, researchers said. There has been a gradual increase in multiple-victim homicides, though the statistics are still low: 3.1 percent of murders in 1976 and 4.4 percent in 2005, according to the Bureau of Justice Statistics. That statistic includes all homicides with multiple victims, not only sprees like that in Aurora.

The larger the group of people psychologists can study, the more they can delve into causes of behavior, and the more sure they can be of their results. Mass killers just aren't very common.

Compounding the problem, Farley said, is that most psychological tests and theories are based on more or less normal psychology. It's a paradigm that can explain things like happiness, depression and anxiety, but it doesn't work as well when faced with extreme cases, he said. [Top 10 Controversial Psychiatric Disorders]

"I worry that we may not even be able to get a good fix, in a sense, on his mental health status," Farley said of Holmes. "There just aren't enough reference points."

Though little information has been released on Holmes' mental health, Farley said he'd be surprised to find out that the alleged shooter was psychotic, given the months of planning that went into his spree.

Calling for prevention

Farley and others contacted by LiveScience could only speculate on Holmes' motives, given the scant information available about the case. There have been shootings in the past by struggling graduate students, Farley said, citing a 1991 murder-suicide at the University of Iowa in which a friend of Farley's along with four other professors were killed. The pressure of living up to expectations in graduate school can be very stressful, Newman said, potentially exacerbating violent tendencies.

There are other questions to ask as well, Farley said, from how socially isolated Holmes was to why he may have developed a focus on the Batman franchise, dying his hair a Joker-like shade of red (Batman merchandise was also found in Holmes' apartment).

Psychologists interviewed for this story agreed that the pressing problem is to find a way to prevent these killing sprees before they happen. Even in people who will never snap, the problems of social isolation and feelings of insignificance are terrible burdens, Newman said.

"It's not so much to catch shooters, because we know that's very difficult, but actually to address very widespread problems that reach millions of kids," she said.

Though the U.S. homicide rate has dropped in the last decade or so in the U.S., psychology should also focus more on less headline-grabbing violence, Farley said, arguing for a concerted effort to study what he called the "heart of darkness" in humanity.

"I sit here in Philadelphia with 400 homicides a year," Farley said. "It's not just mass murders. It's just everyday slaughter."