Something unusual happened in Alabama Friday afternoon. A woman committed mass murder.

She opened fire in a biology faculty meeting at the University of Alabama’s Huntsville campus. Police took Dr. Amy Bishop, a Harvard-trained scientist, into custody unharmed, on suspicion of killing three faculty members and seriously wounding three other adults.

"There is no accurate or useful profile of students who engaged in targeted school violence," according to a study of school shootings by the Secret Service and the Department of Education.

This was not the first woman to be suspected of committing mass murder, but she’s a rarity. A female shooter upends the “profile”—the now-famous staple of so many crime shows—contradicting one of the few elements of that is actually accurate. The prevailing notion that spree shooters are typically affluent, white, outcast loners is a complete myth. "There is no accurate or useful profile of students who engaged in targeted school violence," according to the definitive study of all "targeted" school shootings in the U.S. in a recent 26-year period conducted by the Secret Service and Department of Education.

Other experts on mass murder have come to similar conclusions. But the perps are almost always male. In the school shootings studied by the Secret Service, 100 percent of the shooters were men. (The report's rigorous inclusion criteria eliminated some shootings, but provided an extensive and focused data sample.)

Still, there have been exceptions to the rule. In 1979, 16-year-old Brenda Ann Spencer shot up a school from the window of her own home, killing two students and wounded nine others at Grover Cleveland Elementary school in California's San Diego County. She was denied parole for the fourth time last fall. And two years ago, a woman fatally shot two students before turning the gun on herself at Louisiana Technical College in Baton Rouge.

Local media reported that the University of Alabama shooter Friday was a professor who had previously been turned down for tenure and was just informed that she had lost her appeal. So it’s quite possible that this was an episode of workplace violence (a.k.a. “going postal”). The school setting might have been arbitrary in her mind, aside from it being her place of employment. However, there have been a disturbing number of incidents the past several years in which adults seem to have targeted schools because shootings in those settings generate headlines. It’s way too early to know the suspect’s motives, and important not to settle on any one conclusion.

If the suspected shooter was denied tenure, many will conclude that she “snapped” from the rebuke and exacted revenge. But that theory is at odds with the fact pattern that plays out in many mass murders. Most are pre-mediated, which was almost surely the case here. Assuming she didn’t ordinarily attend faculty meetings armed, she knew what she intended in advance. That’s also the norm. The Secret Service found that a whopping 93 percent of the shooters it studied planned their attacks in advance. The planning phase varied from several hours to a few days, to six to eight months. (The Columbine killers famously planned for over a year.) More than two-thirds of the shooters planned for at least two days. “Several findings of the Safe School Initiative indicate clearly that the school-based attacks studied were rarely impulsive. Rather, these attacks typically were thought out beforehand and involved some degree of advance planning,” the study found.

Shooters often have complex motivations, but the vast majority attack after a serious failure or loss. This occurred in 98 percent of the cases studied by the Secret Service; two-thirds of the time, a loss of status was involved. And in 61 percent of the cases, revenge was a factor.

Dave Cullen is the author of the Edgar-nominated book Columbine. More government research on school shootings can be found at http://davecullen.com/columbine/columbine-guide/evidence-columbine.htm and http://www.fbi.gov/publications/school/school2.pdf.