On July 22, Ali David S. struck the Olympia shopping mall in Munich, exactly five years after right-wing extremist Andres Breivik killed 77 people in Norway. There is a possibility that the Norwegian was a role model for the Munich killer.

Statistician Sherry Towers of Arizona State University has looked into what she calls "the contagion effect" of mass shootings.

Towers' team determined that mass killings - events with four or more deaths - created a "contagious" period that lasted an average of 13 days. One attack at a school seemed to spark the idea in other vulnerable youth.

This kind of "contagious thinking" is not implausible, Towers says. Young people could be susceptible to the idea of suicide if they read about it in the media. There are also indications that reports on murder and suicide lead to an increase in those crimes, she explains.

"It occurred to us that mass killings and school shootings that attract attention in the national news media can potentially do the same thing, but at a larger scale," Towers says in a statement about the 2015 study.

Identification with killers

"Mass killers are always copycat murderers," the Action Alliance School Shooting Winnenden tells DW, adding that "they look for role models, who they emulate and even want to surpass."

Mass murderers plan their attack weeks in advance, says Britta Bannenberg, lawyer and criminologist in Giessen in southern Germany. Many of them write diaries or invent stories, in which they describe the incident. They surround themselves with real and fake weapons, write farewell notes and think about what they will wear during the shooting.

They read about other such incidents, look at documentaries and videos," Bannenberg explains, adding that the killers also play target video games, also known as ego-shooters, to imagine for themselves how it would be to implement their plan.

The media is indispensable for copycat attackers because it provides information about previous killings. News outlets play an important role because the attacker identifies with figures of revenge and role models who have committed similar crimes in the past, Bannenberg says.

A word of caution

News organizations need to pay attention to the choice of words while reporting on such incidents, says Loren Coleman, author of the book "The Copycat Effect: how the media and popular culture trigger the mayhem in tomorrow's headlines."

According to Coleman, one should not, for example, report on "successful" gun attacks or "failed" suicides. Stereotypes such as "the boy next door" or "loner" should also be avoided, he adds.

Journalists need to ensure that they report objectively on such events, says German psychologist Jens Hoffman, referring to the 19-year-old killer who shot down 16 members of his school in Germany's Erfurt in 2002.

"If young killers like Robert Steinhäuser are neither demonized nor presented as innocent, then their biographies will depict the inner conflict and their weakness. In this manner, the mass murderer's function as a role model can be diminished."