The Kouachi brothers, who allegedly spearheaded the massacre at the French satirical publication Charlie Hebdo, are yet another in a long line of terrorist siblings.
The Tsarnaev brothers, Dzhokhar and Tamerlan, are the alleged 2013 Boston Marathon bombers.
Of the 19 hijackers on Sept. 11, 2001, six were brothers, with pairs on the same flights. The U.S. government said Hamza and Ahmed al-Ghamdi were on United Airlines Flight 175, Waleed and Wail al-Shehri were on board American Airlines Flight 11 and Nawaf al Hazmi and Salem al Hazmi helped hijack American Airlines Flight 77.
And in 2002, three brothers — Ali Imron, Amrozi Nurhasyim and Ali Ghufron — were named as being responsible for three bombings in Bali.
Sibling teams have long been linked to terrorism, analysts say.
According to analysts Mia Bloom and John Horgan at the University of Massachusetts Lowell's Center for Terrorism and Security Studies, the Irish Republican Army, for example, boasted several brother teams among its ranks. Other European terrorist groups had siblings or relatives.
Bloom and Horgan’s paper on the topic of sibling terrorists gives several reasons for siblings to join terrorist groups or plot a terrorist attack.
They are likely to share perceived grievances, the authors said.
As an example, the authors say Palestinian children whose house was destroyed by Israel might come away from that experience ready to commit terrorist acts and "may even be deployed for the same mission."
The authors found that "family members can help sustain both the commitment of participants as well as heighten operational security."
"There’s an echo chamber between siblings," Bloom said in an interview. "They bounce radical views off each other" and become more radicalized.
Bloom added that family members are less likely to inform on one another. As for suicide bombing, one sibling likely would prevent another from a change of mind.
Marc Sageman, author of the book “Understanding Terror Networks," which profiled 172 jihadists, said that among the people he studied, 20 percent were relatives and 70 percent were friends.
"If you look at the history of political violence, it was mostly small groups of people who know each other before, including relatives who defied the state," he said. "They develop a common social identity. It happens in gangs, on street corners … any group that categorizes as a group."