If Yvonne Hiller killed her coworkers at the Kraft Foods baking plant in Northeast Philadelphia last week as charged, she would join a rare - but possibly emerging - breed: women as workplace killers.
Women commit fewer than 5 percent of homicides and assaults in the workplace, said Larry Barton, a teacher at the FBI Academy and author of four books on crisis management and violence at work.
And, as a rule, they're much less likely to kill in general than men. They tend to internalize their anger or use words rather than haul out a gun in a public place and open fire, experts say.
But in the last year, several high-profile cases of women killing in the workplace have occurred, including a professor accused of killing three colleagues and wounding three others in a February rampage after being denied tenure at the University of Alabama in Huntsville.
"I cannot recall a one- or two-year period in which we've had as many women with multiple victims," said Barton, who is also a professor at the American College, a risk-management and insurance school in Bryn Mawr.
In March, a Tarpon Springs, Fla., supermarket worker fired for threatening to kill a coworker returned to work and made good on her threat.
And though not as recent, in January 2006 a former U.S. Postal Service employee killed six colleagues and then herself at a mail-sorting plant in Goleta, Calif.
"Is it too early to call it a trend, or is it just an anomaly?" Barton wondered.
In the Philadelphia case, Hiller, 43, is charged with killing LaTonya Brown, 36, and Tanya Wilson, 47, both of Philadelphia. She is also accused of shooting coworker Bryant Dalton, 39, in the neck; he was in critical condition at Thomas Jefferson University Hospital.
Police said Hiller, in an ongoing dispute with her colleagues, had accused them of talking behind her back and spraying her with chemicals. She was suspended Thursday night and sent home after an argument with those coworkers. She returned and pressed her way in by holding two unarmed security guards at gunpoint, authorities said.
She found her targets in a break room and opened fire, police said.
Women are much less likely to kill than men, statistics show. A study by the University of Tennessee found that women committed 15 percent of homicides, though they make up more than half the U.S. population.
Women are much more likely to target spouses, intimate acquaintances, or relatives, the study also found.
"Females are often socialized to see their behaviors more in the context of the implications it has for other people," said Carter Hay, an associate professor of criminology and criminal justice at Florida State University in Tallahassee. "Males have been socialized to be more aggressive, more willing to take risk, more willing to take aggressive, bold action when they feel they've in some way been violated."
Steve Albrecht, coauthor of Ticking Bombs: Defusing Violence in the Workplace, said women were more likely to kill their children, themselves, or the men who beat them.
"But it is quite rare for them to engage in violence against strangers or people they know" casually, he said. "It says a lot about this society that women would make that kind of leap to this illogical behavior. Men have been doing this since the caves."
Workplace homicide - committed by either gender - is rare.
In 2009, there were 521 workplace killings in the United States, 420 of them committed by gunfire, according to the U.S. Bureau of Labor Statistics. Of those, 24 were in Pennsylvania and 18 in New Jersey.
The bureau did not have information on how many were committed by women.
The vast majority of killings on the job, according to Northeastern University criminologist James Alan Fox, involve robberies - including taxicab holdups and convenience-store stickups - and assaults on police and security officers. Others result from domestic disputes that spill over into the workplace, he said.
Disgruntled employees or ex-employees commit fewer than 100 workplace homicides annually, he said. Women account for a small number of those, he said.
"Men tend to look at violence as an offensive weapon, women as a last resort," he said.
From childhood, boys express aggression differently than girls do, said Nadine Kaslow, professor and vice chair of Emory University's department of psychiatry in Atlanta. Girls do it with words, boys with fists.
Men are also more likely to use violent means to kill.
"Men tend to be more comfortable with physically violent forms of aggression," she said.
As for the reason more women may be committing workplace violence, she said: "What we're seeing, particularly as the economy has gotten difficult, is that more and more people are resorting to violence as a coping strategy. They feel so trapped that they feel the only way to respond is to be violent. I think women are getting swept up in that, too."
Contact staff writer Susan Snyder at 215-854-4693 or firstname.lastname@example.org.
Inquirer staff writer Jane Von Bergen contributed to this article.