After the suspects in the San Bernardino massacre were killed in a shootout with police, criminal justice experts and stunned observers alike were both struck by the unusual nature of the attack. It involved two shooters, and perhaps more remarkable, one of the alleged assailants was a woman.
While the motives of the female suspect - identified as 27-year-old Tashfeen Malik - and her husband remain unclear, the attack is certainly an outlier in the United States. Of 160 active shootings in the U.S. between 2000 and 2013, only six involved a female shooter, according to FBI statistics.
"The bad actor tends to be the man more than the woman, usually," said Eugene O'Donnell, professor of law and policy studies at the John Jay College of Criminal Justice.
Yet overseas, a growing number of women are active participants in high-profile attacks - from Nigeria and Russia to Iraq and France.
Just last month, a 26-year-old daughter of a Moroccan immigrant was among three people killed in a Belgium raid targeting Abdelhamid Abaaoud, the suspected architect of the attacks in Paris. The woman, Hasna Aitboulahcen, was believed to have been Abaaoud's cousin and his accomplice.
While Aitboulahcen did not detonate a vest, as initially believed, the prevalence of female suicide bombers is well documented worldwide. Anti-government Kurdish women have blown themselves up in Turkey; Palestinian women have carried out suicide attacks against Israelis; and female suicide bombers from Chechnya are so prevalent, they gained a nickname in Russia: "black widows."
Last month, Moscow revealed that it had thwarted a plot by female suicide bombers to attack the 2014 Sochi Olympics by sneaking explosives disguised as hand cream on an airliner.
Islamic extremist groups - including al Qaeda in Iraq and Boko Haram and al-Shabab in Nigeria - have all deployed female suicide bombers.
Mia Bloom, a Georgia State University professor and the author of "Bombshell: Women and Terror," said that Islamic groups have embraced women for several reasons, including an evolving religious ideology that equates the jihad responsibilities of men and women. But their role has also increased for obvious tactical reasons.
"Women are ideal operatives when attacking soft targets and blending in with civilians," Bloom wrote. "As terrorist organizations have shifted from attacking military targets (hard targets) to civilian targets (soft targets), women have been especially useful."
While ISIS says it forbids the use of women as suicide bombers, it does have a brigade of female fighters known as Khansaa and it has managed to lure women from other countries to be would-be jihadis.
In June, British police said three women and their nine children may have joined another relative already fighting with ISIS in Syria. Earlier in the year, British detectives were criticized for failing to prevent three 15- and 16-year-old London girls from making the same journey.
But could the wave of female attackers take hold on U.S. soil? The evidence is scant but the social media pull of ISIS is growing in America.
According to a new report, at least 300 Americans are spreading ISIS propaganda for the terrorist group and actively recruiting individuals on Twitter. Nearly a third of the social media accounts examined appear to be operated by women.