As the public struggles to uncover the reasons behind the eight seemingly senseless mass murders so far this year, many researchers are working to determine whether this apparent surge in violence indicates a larger trend, and whether to expect more in the months to come.
Mark Kopta, chairman and professor in the department of psychology at the University of Evansville in Indiana, has researched extensively the country's mass killings, which he defines as attacks leading to the deaths of at least five people, including the killer's suicide.
"This is not a savory subject," Kopta said.
But, he added, it may be one that is becoming increasingly relevant to the U.S. public. In a paper to be presented at the annual meeting of the Midwestern Psychological Association in Chicago this month, he found three incidents in the United States fitting this profile between 1930 and 1970. Three more followed over the course of the 1970s.
In the 1980s, however, there were 10 such incidents of mass murder. The 1990s had 17; and, since the new millennium began, there have been 25 such mass murders.
Six of them occurred last year. And 2009 has already topped that with eight such killings.
Police believe Ervin Lupoe of Los Angeles fatally shot his wife, his five children and himself Jan. 27 after faxing a note to a local television station claiming the couple had just been fired from their hospital jobs. A Cleveland man, Davon Crawford, killed his newlywed wife, his sister-in-law and three young children March 5 before shooting himself to death when cornered by police.
The four mass shootings in March made it the bloodiest month yet this year. Michael McLendon of Kinston, Ala., killed 10 people -- five family members and five other people -- before committing suicide March 10 in a factory in which he formerly held a job. Guillermo Lopez of Miami opened fire at a party March 15, killing his estranged wife and three other people before returning to his apartment, setting fire to it and shooting himself.
Five days later, Robert Stewart entered a nursing home in Carthage, N.C., March 20 and opened fire on residents, killing seven of them along with one nursing home employee. And Devan Kalathat, an engineer at Yahoo living in Santa Clara, Calif., fatally shot his two children and three other relatives March 29 at a family party before turning the gun on himself.
The first six killings set the stage for two more tragedies so far this month, the first an April 3 rampage in which Jiverly Wong entered an immigration center in Binghamton, N.Y., armed with two handguns. Police told the Associated Press that the man fired 98 shots, killing 13 other people before taking his own life.
The country's latest mass shooting occurred in the early hours of Saturday morning, when James Harrison of Graham, Wash. killed his five children before driving to a nearby casino and shooting himself inside his car. Authorities told the Associated Press that Harrison committed the murders after he learned from his wife that she was planning on leaving him.
By Kopta's count, the Binghamton shooting pushed 2009's mass murder total beyond the six of 2008. Still, the overall number of these incidents remains relatively small, which makes it difficult to draw any solid conclusions on the reasons behind the shootings.
"We don't have enough data to say anything for sure; the numbers are too small," he said. "Right now, it looks like a trend. Is it a temporary trend? We don't know."
Grant Duwe, criminologist with the Minnesota Department of Corrections in St. Paul, agreed that it is far too early to divine a solid pattern underlying the recent spate of high-profile shootings.
"It's difficult to know for certain why there appears to be a recent increase in mass murder and, more narrowly, mass public shootings," Duwe said.
Plus, he noted, mass murder is all about how you define it. In his 2007 book, "Mass Murder in the United States: A History," Duwe takes a look at incidents in which four or more victims were killed within a 24-hour period, and in which the killer was not necessarily suicidal. Using this formula, he examined 909 such murders in the United States that took place between 1900 and 1999.
As opposed to Kopta's figures, in which mass murder cases progress from a flat line through the 1970s to a rapidly ascending curve in the 1990s, Duwe's graph looks more like a saddle, with more mass shootings occurring before and after a pronounced trough in the 1940s and 1950s.
"In my book, I argue that the trough in the mass murder rate during the 1940s and 50s may have been due to the upsurge in pro-social indicators like marriage, family, jobs, college attendance, home ownership, church attendance and an overall higher standard of living," he said. "Although the rise in pro-social indicators did not deter everyone from committing mass murder, it may have dissuaded those at the margins."
But even Duwe said that this model, too, presents far more questions than answers. "It's important to emphasize that this is speculative, as empirical research is still needed to better identify the causes and correlates of mass murder," he said.
The lack of solid answers has not quelled speculation within the public as to the reason for this year's early cluster of mass murders. Much of this speculation revolves around the economic downturn, particularly when it comes to the cases in which the shooter had recently lost a job or was otherwise facing financial hardship.
But Jeffrey Adler, a professor of history and criminology at the University of Florida in Gainesville, said that, historically, this explanation does not work well.
"Throughout U.S. history, murder has not increased when the economy has taken a downturn," Adler said. "For example, the 1930s [the time of the Great Depression] may have been the safest decade in American history.
"It's too easy and too formulaic to say that this is a response to the downturn in the economy," he continued. "If that's the case, then other depressions in U.S. history should have left the nation awash with blood, which they didn't."
Likewise, other external factors, such as discontent with the government, or the disenfranchisement of a racial group, provide no simple template that ensconces all of this year's violent episodes. Indeed, a look at the eight mass murders so far this year reveal that some seem to have been sparked by domestic disputes, while others appear to have been triggered by social isolation, and others still seem completely random.
"This does not fit a single pattern, or even two or three patterns," Adler said.
But what does seem to be a common thread is anger. And Kopta said that uncovering the roots of this anger is critical to understanding these tragedies.
"Anger is the most seductive emotion of all," he said. "When people get angry, they don't want to stop being angry."
In his research, Kopta identified one potential source as media influence.
"We have not targeted any specific content," he said. "But some of it is very dark; it has to do with hatred of other people, or how unfair the world is."
It is a point with which Duwe disagrees. Rather, he said his research identifies 10 common threads that appear to link mass public shooting throughout U.S. history, including mental illness, social isolation, a motive of revenge and a triggering event that ultimately sets the horrific deed into motion.
Other patterns, such as a seeming increase during particular months, are most likely spurious, Kopta said.
"Is there something about March that makes people more at risk? I wouldn't think so," he said. "I would be careful creating patterns that aren't necessarily consistent with what is happening."
The unpredictable nature of mass murders makes preventing them a nearly insurmountable challenge, the researchers said. Still, some maintain that the United States can take steps to reduce the likelihood of such tragedies -- and few are more vocal than those with the Brady Campaign to Prevent Gun Violence.
"This particular month has just been a catastrophe for folks who do what we do; it's been a rough month," said Doug Pennington, spokesman for the Brady Campaign. "People aren't interested as much in what we have to say until something like this happens."
But he said the fact that all of these killings involved firearms offers a glaring clue as to what might be done to curb these episodes.
"From our perspective, we have encountered events like this for so long, and we interpret events like this less from the root causes and concentrate more on a common denominator," he said. "You don't have these events without a dangerous person getting their hands on a firearm. ... They're not using baseball bats, they're not using Frisbees, they're not using knives, they're not using any other weapons."
He said that the top three agenda items for the Brady Campaign are to enforce criminal background checks on all gun sales, to limit the bulk sales of handguns and to limit the availability of military-style assault weapons.
Still, several of this year's mass murders could have still occurred, even if all three of these measures had been in place. Pennington said this fact underscores the need to talk about gun sales to mentally disturbed individuals.
"We could have an open-ended discussion in this country about the Jiverly Wongs of this world," he said. "The mental health aspect is not a part of our core agenda right now, but it could be if we all, as a country, had a conversation about it."
Associated Press reports contributed to this story.