“It is shocking,” said Penn State psychology professor Marissa Harrison, the lead author on the study, in a telephone interview with The Washington Post. “The profile we put together sounds just like your average person. … There is no way to tell.”
Harrison and her colleagues spent months combing newspaper reports dating back to the Revolutionary War to find every recorded instance of a female serial killer. (Though definitions vary, Harrison considers a “serial killer” anyone who kills three or more people with a “cooling-off period” of a week or more between each murder.)
Beginning in 1821 with Martha “Patty” Cannon – the “she-demon” leader of a gang, according to contemporary newspaper reports, who committed at least four murders in the course of her usual business of kidnapping people and selling them into slavery – the study examines the backgrounds, motives, methods and mentality of 64 women serial killers in American history.
Although female serial killers, like unhappy families, are each horrifying in their own way, Harrison found some striking similarities among her subjects. Most of them came from fairly mundane backgrounds, their primary weapon was poison, and nearly all of them killed people they knew, often their own family members. By comparison, most victims of male serial killers are unknown to their murderer.
“Female serial killers gather and male serial killers hunt,” Harrison said. “That was very interesting to me, as an evolutionary psychologist, that it reflects kind of ancestral tendencies.”
Harrison also saw evidence of evolutionary influences in what drove women to kill. While most murders by male serial killers tend to involve sex in some way — a 1995 study found that male serial killings are characterized by a desire for domination, control, humiliation and sadistic sexual violence — women are more likely to kill for money or power.
“It struck me that women would kill for resources, which was their primary drive in the ancestral environment, and men kill for sex,” she said.
Most of the serial killers played up gender roles to their advantage. About two-thirds of them for whom data was available were described as having average or above average attractiveness, which the study says they exploited to elude suspicion. They also took on jobs in stereotypical feminine professions — nursing, care giving, teaching — that gave them access to vulnerable victims. And they were often given dainty or girlish nicknames that are jarringly dissonant with the horror of their crimes.
Take, for example, “Jolly Jane” Toppan, a nurse at Cambridge Hospital in Massachusetts. In 1901, she confessed to having poisoned dozens of victims — among them at least 12 patients, her landlords, her foster sister and her childhood friend. She is said to have later told police: “That is my ambition, to have killed more people — more helpless people — than any man or woman who has ever lived.”
Or the “Death House Landlady,” Dorothea Montalvo Puente, a grandmotherly looking woman who ran a boarding house for the elderly. Puente would cash their social security checks for her own use, and kill all those who complained. A police investigation unearthed seven bodies buried in her backyard.
One outlier was Aileen Wuornos, perhaps America’s most famous female serial killer. Rather than the elderly or ill, Wuornos’s victims were men who she shot and left along the sides of highways. But Wuornos spoke about the killings with the same chilly brutality as Toppan: “I robbed them, and I killed them as cold as ice, and I would do it again, and I know I would kill another person because I’ve hated humans for a long time,” she said.
Female serial killers are a rarely studied phenomenon, according to Harrison, perhaps because of culturally ingrained notions that women would be incapable of such crimes. But this can be a deadly misconception.
In her study, she wrote that unwillingness to believe the idea of a woman serial killer may allow murderers to get away with their crimes — on average, female serial killers are able to evade arrest for twice as long as men are. Their victims pay for that extra time.
“Contrary to preconceived notions about women being incapable of these extremes, the women in our study poisoned, smothered, burned, choked, bludgeoned and shot newborns, children, elderly and ill people as well as healthy adults; most often those who knew and likely trusted them,” the study read.