This undated photo provided by the San Bruno Police Department shows Nasim Aghdam. Law enforcement officials have identified Aghdam as the person who opened fire with a handgun, Tuesday, April 3, 2018, at YouTube headquarters in San Bruno, Calif., wounding several people before fatally shooting herself in what is being investigated as a domestic dispute, according to authorities. (Photo: Courtesy of San Bruno Police Department via AP)

Police rushed to YouTube headquarters in San Bruno, California, this afternoon (April 3), after reports of an active shooter there. Police said they arrived to a "very chaotic scene" as employees fled the building.

The shooter is reportedly dead from a self-inflicted wound, and four victims are being treated at a nearby hospital, according to news reports.

Though mass shootings seem less likely to evoke shock and awe these days — with 2018 having several such shootings logged already, according to an online tracker — there is one surprising aspect of the YouTube shooting: The shooter was a "she."

That's shocking, according to experts in human behavior, because women are violent at much lower rates than men. And mass killings, even more so than other types of violence, are overwhelmingly a male phenomenon.

Female mass killers are "so rare that it just hasn't been studied," said James Garbarino, a psychologist at Loyola University Chicago who has researched human development and violence. 

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