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.
