A young Amy Bishop. Courtesy the Bishop family.

One winter day in 1961, in Newark Valley, New York, the young couple Tim and Waneta Hoyt experienced a horrible tragedy. Their first child, Eric, who was not yet three months old, suddenly died. The precise causes of infant mortality are sometimes mysterious, and doctors could find no obvious explanation for Eric’s death—he had simply stopped breathing. The following year, Waneta gave birth to another boy, James. But he, too, abruptly died. It was only after the couple lost a third infant, Julie, in 1968, that Tim and Waneta turned to Alfred Steinschneider, a medical researcher in Syracuse who specialized in Sudden Infant Death Syndrome, or SIDS.

After examining the case history, Dr. Steinschneider concluded that SIDS could be genetic, which would explain the deaths of multiple infants in the same family. Waneta gave birth to two more children, Molly and Noah, both of whom died while under Steinschneider’s care. In 1972, Steinschneider published a landmark paper in the journal Pediatrics, in which he argued that SIDS could be hereditary, and was related to sleep apnea. The paper was a great success, and sales of sleep monitors—which Steinschneider recommended—took off. For twenty years, the Hoyts, who were described in the paper simply as “the ‘H’ family,” served as a sad exemplar in medical literature.

However, in the early nineties, a district attorney in upstate New York, who had been tipped off by a suspicious forensic pathologist, took a closer look at Steinschneider’s paper and opened an investigation. As Richard Firstman and Jamie Talan recount in their book, “The Death of Innocents,” under questioning by police in 1994, Waneta Hoyt confessed that her children had died not from SIDS but, rather, because she had smothered them. She later recanted this confession. But, in 1995, she was convicted of killing all five children and sentenced to seventy-five years in prison.

On the surface, this case might seem unrelated to the story of Amy Bishop, which I recount in a piece in the current issue of the magazine (“A Loaded Gun”). One theme of the Bishop saga is the dangerously formidable power of parental love, which seems a far cry from Waneta Hoyt, who dispatched her own children, one by one. But the two cases share a common, troubling thread: neighbors, police officers, and even the medical establishment may be more likely to overlook glaringly suspicious behavior when the perpetrator of that behavior is a woman.

In the aftermath of the massacre at Sandy Hook Elementary School, last December, there has been much public discussion about the necessity of greater vigilance regarding mental-health issues—about our ability to recognize red flags early and get potentially dangerous individuals into treatment. It’s a reassuring notion, and less divisive, certainly, than calls for greater gun control or for censoring video games. But, as the Bishop story makes clear, this kind of early-warning system is often difficult to institute in practice. Amy Bishop shot her own brother, after all. She punched a woman at a pancake restaurant. She stood accused of mailing a bomb to one of her supervisors at Harvard. Red flags don’t get much brighter than that. Yet, nobody stepped in. Why not?

One answer, which I explore in the piece, is the role that collective denial can play, not just in families but in communities and local institutions, like police departments. But another answer may lie in Bishop’s gender. In a 1998 article about gender bias in the criminal-justice system, Larissa MacFarquhar, reviewing two books about female killers, observes, “The message that emerges from this collection of tales is clear enough: be a woman, act like a woman, and you may blithely strew your neighborhood with bloody axes and severed heads, since the chances are that you will get away with murder.”

In her article, MacFarquhar relates gruesome tales of so-called Black Widows (women who murder their husbands or lovers) and Angels of Death (women who kill those placed in their professional care). These women often skirt suspicion and kill prolifically because it doesn’t occur to the cops until much, much too late that a female could be capable of such a thing. In retrospect, the crimes seem gallingly obvious: Genene Jones, an Angel of Death who worked as a pediatric nurse in Texas, is believed to have murdered as many as forty-six children before authorities caught up with her, in 1983. But as the murders are actually being committed, investigators prove far too ready to attribute the mounting body count to accidents, medical error, or a male perpetrator.

The detection of crime, as MacFarquhar notes, is “one of the most stubborn redoubts of male chauvinism.” Women have fought to undo the patriarchal notions of gentle femininity that in the past have excluded them from suffrage, employment, and combat roles in the military. But, in the criminal-justice system, they may still be construed as lacking in the moral and physical agency that is necessary to carry out a violent crime.

Consider the case of Karla Homolka, a young Ontario woman. In 1991, she married an accountant, Paul Bernardo. They were an attractive, apparently happy couple, but, in 1993, Canadian authorities began to suspect Bernardo in a string of unsolved rapes. Investigators also linked Bernardo to the recent rape and murder of two local schoolgirls. When Homolka was questioned by police, she informed them that her husband was indeed responsible for the crimes, and that he had beaten her savagely and forced her to become an accomplice. Homolka made a sympathetic witness—a middle-class white woman who worked at a veterinary clinic and had been battered by her domineering spouse. She had also suffered a recent tragedy: in 1991, her fifteen-year old sister, Tammy, had died after she passed out from drinking too much champagne at a Christmas party and choked on her own vomit.

Because Homolka had known about her husband’s crimes and played some role in them, prosecutors could not offer her full immunity. But they struck a plea bargain in which she agreed to testify against Bernardo in exchange for a light sentence. In assessing her culpability, Canadian investigators were reportedly influenced by a paper, written by Roy Hazelwood, an F.B.I. profiler, called “Compliant Victims of the Sexual Sadist.”

It was only after Homolka’s deal was in place that she provided a fuller confession, explaining that she had not merely been a witness to Bernardo’s crimes but an active participant as well. Home videos that showed Homolka’s role in the sexual assaults to be anything but forced surfaced not long afterward. And it ultimately emerged that Tammy’s death was not an accident: Homolka had drugged her sister with an animal tranquilizer that she had stolen from work, then she and Bernardo had raped her.

To be sure, women are less apt to commit crimes—especially violent crimes—than men are; that has long been an accepted criminological fact. In recent decades, the “gender gap” in crime has narrowed somewhat, however, and there are a number of theories that might account for that change. Some believe that women are committing more crimes than they have in the past, but others argue that women are simply being investigated and arrested more often, as cops gradually come to terms with the concept of a female criminal.