A 1999 study by Dr. Mullen and others in the Archives of Suicide Research suggested that a 10-year outbreak of mass homicides had occurred in clusters rather than randomly. This effect was also found in a 2002 study by a group of German psychiatrists who examined 132 attempted rampage killings world-wide. There is a growing consensus among researchers that, whether or not the perpetrators are fully aware of it, they are following what has become a ready-made, free-floating template for young men to resolve their rage and express their sense of personal grandiosity.
Whatever the witch's brew of influences that produced this grisly script, treating mass killings as a kind of epidemic or contagion largely frees us from having to understand the particular causes of each act. Instead, we can focus on disrupting the spread.
There is a precedent for this approach in dealing with another form of violence: suicides. A 2003 study led by Columbia University psychiatrist Madelyn Gould found "ample evidence" of a suicide contagion effect, fed by reports in the media. A 2011 study in the journal BMC Public Health found, unsurprisingly, that this effect is especially strong for novel forms of suicide that receive outsize attention in the press.
Some researchers have even put the theory to the test. In 1984, a rash of suicides broke out on the subway system in Vienna. As the death toll climbed, a group of researchers at the Austrian Association for Suicide Prevention theorized that sensational reporting was inadvertently glorifying the suicides. Three years into the epidemic, the researchers persuaded local media to change their coverage by minimizing details and photos, avoiding romantic language and simplistic explanations of motives, moving the stories from the front page and keeping the word "suicide" out of the headlines. Subway suicides promptly dropped by 75%.