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."