The Tsarnaev brothers wreaked carnage in Boston. The Kouachi brothers attacked Charlie Hebdo magazine offices in Paris. In Brussels, officials say the El Bakraoui brothers struck the airport and metro March 22, 2016, killing more than 30 people.
Blood ties have long been a feature of criminal networks, from the outlaws Frank and Jesse James to the family structure of the Mafia. The phenomenon extends to terror plotters for reasons that experts say are both logistical and social.
Ibrahim and Khalid El Bakraoui, seen here on the front page of a Belgian newspaper, have been identified by a Belgian prosecutor as two of the bombers who killed more than 30 people in Brussels on March 22, 2016. Elder brother Ibrahim, 29, blew himself up at the airport. Khalid, 27, detonated his bomb at the Maelbeek subway station.
The El Bakraoui brothers were known as criminal thugs to Belgian authorities, but it's not clear how much more authorities knew of their activities. Turkish officials say the older brother was caught in June at the Turkish-Syrian border and deported to the Netherlands. Turkey says it warned both Belgium and the Netherlands that he was a "foreign terrorist fighter."
Salah Abdeslam & Ibrahim Abdeslam
Brussels-born brothers of Moroccan descent -- (L) Salah Abdeslam and Ibrahim Abdeslam -- were two of the attackers who killed 130 people in gun and bomb attacks in Paris on November 13, 2015.
Ibrahim, 31, blew himself up outside a cafe, while 26-year-old Salah, who had handled a car rental and other logistics, fled Paris on the night of the attacks. He was arrested March 18, 2016 in Brussels..
The brothers had run a bar in Brussels' Molenbeek district, a neighborhood with links to several recent jihadi plots. Both had served jail time for petty crimes - it was in prison that Salah met Abdelhamid Abaaoud, who would become the ringleader of the Paris attacks.
This video image taken from a CCTV camera at a gas station in Ressons, North of Paris, on November 11, 2015 shows Salah Abdeslam (R), a suspect in the Paris attack of November 13, and Mohamed Abrini (C), a 30-year-old Moroccan Belgian, suspected of having participated in scouting out the attack sites with Abdeslam, buying goods.
Chérif & Said Kouachi
Paris-born Said Kouachi, 34, and his 32-year-old brother Chérif stormed the office of satirical newspaper Charlie Hebdo in the French capital in January 2015, shooting a dozen people dead. They were killed two days later in a police raid on their hideout outside Paris.
As children they spent time in state care after the death of their mother; as adults they drifted into low-paying jobs, petty crime and a circle of Islamic radicals. Their links to Islamic militants brought them to the attention of authorities years before the Charlie Hebdo attack.
Chérif was stopped from going to Iraq in 2005 and jailed in 2008 for helping to send militants to fight U.S. forces in Iraq. Said had spent time with an al Qaeda affiliate in Yemen.
"A terror cell made up of two brothers cannot be infiltrated. It's the most secure network possible," said Claude Moniquet, a French security analyst who works in Brussels.
Mohamed & Abdelkhadar Merah
Frenchman Mohamed Merah, 23, Abdelkader's younger brother killed three French soldiers in two attacks March 11 and March 15 in southwestern France. In a subsequent attack on March 19 on a Jewish school in Toulouse he killed four people -- three children and a rabbi. Mohamed, a former garage mechanic who claimed allegiance to al-Qaida, died in a hail of gunfire March 22, 2012, after a dramatic 32-hour-long standoff with law enforcement.
Mohamed, of Algerian descent, reportedly told police his shooting spree was an attempt to "bring France to its knees." He was initially thought to be a "self-radicalized" lone wolf, but documents obtained by Le Monde showed a slew of international phone calls and the use of a phone obtained by his mother to avoid surveillance. Abdelkhadar, 33, and his sister, Souad, were known to authorities as having traveled to Afghanistan in March 2011.
An unidentified man with his head covered, believed to be Abdelkader Merah or his companion, sits between masked police officers as they head to the French police's anti-terrorist headquarters in Levallois-Perret, outside Paris, March 24, 2012.
On Feb. 19, 2016, the Paris prosecutor asked that Abdelkadar Merah stand trial for "criminal terrorist conspiracy, theft" in connection with the shootings. Abdelkhadar was charged with complicity in murder, after reportedly admitting to helping steal a scooter used by Mohamed during the attacks.
Tamerlan & Dzhokhar Tsarnaev
Tamerlan Tsarnaev (L), 26, and his younger brother Dzhokhar A. Tsarnaev, 19, wreaked carnage at the Boston Marathon near the finish line on April 15, 2013, killing three and injuring an estimated 264 people.
The two men arrived with their parents from Chechnya in 2004, settling in Cambridge when Dzhokhar was 8 years old. He appeared to fit in immediately. History teacher, Larry Aaronson, at the prestigious Cambridge Rindge and Latin High School -- the same school Matt Damon and Ben Affleck attended - told CBS News Dzhokhar was a great kid. A stellar athlete, Dzhokhar was the captain of his high school wrestling team and he was popular. He became a citizen on Sept. 11, 2012.
Tamerlan & Dzhokhar Tsarnaev
Dzhokhar (L) and older brother Tamerlan Tsarnaev were spotted on surveillance footage along the marathon parade route after the attack.
On the surface, at least, the younger Tsarnaev brother seemed to be thriving in America, but his older brother, Tamerlan, was clearly struggling. The 26-year-old who once had dreams of boxing in the Olympics, representing the U.S., became a devout Muslim and radicalized. His views seemed to have influenced the younger brother.
Dzhokhar Tsarnaev captured
Tamerlan was injured in a gunfight with police on April 19, 2013 after the death of one more victim -- a MIT policeman - then his brother ran him over with a stolen SUV. He died later in the hospital. Dzhokhar was captured after a massive manhunt and sentenced to death May 15, 2015. It was the most closely watched terrorism trial in the U.S. since the Oklahoma City bombing case two decades earlier.
This photo entered as evidence shows the boat where Boston Marathon bomber Dzhokhar Tsarnaev hid after the gunfight with police. Following the shootout with police and Tamerlan's death, the manhunt continued for Dzhokhar, with Watertown and surrounding neighborhoods shut down. David Henneberry went to check on his boat in Watertown in his backyard and saw someone lying on the deck, who turned out to be Dzhokhar.
Dzhokhar, bleeding, had been hiding inside and had carved a note in the boat: "Stop killing our innocent civilians and we will stop."
Waleed & Hassan bin Attash
Waleed bin Attash, from Yemen, is believed to have run an al Qaeda camp in Afghanistan. Both he and his brother, Hassan, are accused of being 9/11 co-conspirators and are detainees at Guantánamo Bay.
A Department of Defense memo stated the belief that Hassan was influenced by his older brothers Abd al-Aziz Hassan and Waleed, a senior member of al Qaeda and a one-time bodyguard for Osama bin Laden.
Hassan ran a safe house and admitted to attending al Qaeda and Taliban training camps.
Waleed & Wail al-Shehri
Waleed M. al-Shehri (L) and Wail al-Shehri, 33, were identified by the FBI as two of the 19 men who took part in the September 11, 2001 attacks, highjacking American Airlines Flight 11. Flight 11 crashed into the North tower of the World Trade Center.
Waleed was thought to be a Saudi national with a range of birth dates provided on documents. It is believed he was in the U.S. beginning in 1994, when he got a Social Security card and a Florida driver's license.
Wail is believed to have been a pilot who lived in Hollywood, Florida and Newton, Mass.
The two men were not immediately identified as brothers after 9/11 because of the very common surname.
Salem & Nawaf al Hazmi
Saudi brothers Salem (L) and Nawaf al Hazmi were part of the group of hijackers onboard American Airlines Flight 77 which crashed into the Pentagon.
According to the National Commission on Terrorist Attacks Upon the United States, Salem, a younger brother of Nawaf, was born in Mecca. Salem's family described him as a quarrelsome teenager. It is believed Nawaf probably recommended him for recruitment into al Qaeda. One al Qaeda member who knew the two said Nawaf pleaded with Osama Bin Ladin to allow Salem to participate in the September 11 attacks.
Tashfeen Malik & Syed Farook
Individual radicalization often comes through close friends and family members, rather than just external teaching and preaching. Sibling bonds are not the only family connections that have played a role in recent terrorist attacks.
(L-R) Tashfeen Malik and Syed Rizwan Farook, a married couple, died in a fierce gun battle with authorities several hours after their commando-style assault on a gathering of Farook's work colleagues at the county's health department in San Bernardino, California on Dec. 2, 2015.
Farook was a 28-year-old American citizen born in Chicago and employed with the San Bernardino County Department of Health. Farook traveled to Saudi Arabia for two weeks in July 2014 to pick up his fiancee, Malik, 27, who is Pakistani, a law enforcement source told CBS News. Malik received a K1 Visa, known as a fiance visa. It's unclear when the visa was issued.
A former coworker of Farook, Chaz Harrison, described him as "very passionate" about his religion, and said that both he and his wife did not want to be in the U.S. According to the FBI, the San Bernardino killers had been radicalized "for quite some time" and had taken target practice at area gun ranges, in one instance just days before the attack that left 14 people dead.
Mohammed Atta & Marwan al-Shehhi
Cousins Mohammed Atta (L) and Marwan al-Shehhi took part in the 9/11 attacks. Atta was identified by the FBI as the man who piloted the first plane, American Airliens Flight 11, to crash into the World Trade Center, hitting the North Tower on September 11, 2001.
Atta had an Egyptian driver's license. He studied in Germany for a time, where he had ties to an Islamic group that planned attacks on U.S. targets. While there he lived with his cousin, Marwan al-Shehhi.
Before they took part in the 9/11 attacks, the cousins trained as pilots at Huffman Aviation in Venice, where they lived together, and practiced on Boeing 727 flight simulators at SimCenter in Opalacka, Florida.