Family members have taken part in atrocities from Sept 11, to Boston bombing and Paris attacks

Two gunmen killed 15 people and injured dozens at Bondi Beach, Sydney, on Sunday evening. Photo / Supplied

Father and son Sajid and Naveed Akram, the main suspects in last weekend’s attack on a Jewish festival at Australia’s Bondi Beach, are far from being the only ones to operate as a family.

Recent examples include brothers Dzhokhar and Tamerlan Tsarnaev, who bombed the 2013 Boston Marathon, and siblings Cherif and Said Kouachi, who were behind the January 2015 attack on the French satirical magazine Charlie Hebdo.

Another set of brothers, Salah and Brahim Abdeslam, were among the 10 jihadists who rampaged across the French capital in November that year, killing 130.

“It’s a longstanding and well-known phenomenon because terrorist indoctrination remains a social phenomenon, and the closest social environment is often the family,” Alexandre Rodde, a terrorism and mass casualty attack analyst, told AFP.

“Among the 19 terrorists who hijacked the planes on September 11, 2001, there were three sibling groups,” said Rodde, from the French National Gendarmerie and Coventry University in the United Kingdom.

Laurence Bindner, a specialist in online extremism, said on the whole there were more “horizontal radicalisations” between siblings than “vertical” ones of parents or children.

But she highlighted the example of Christine Riviere, a Muslim convert nicknamed “Granny Jihad”, who travelled to Syria three times in support of her jihadist son, Tyler Vilus.

Vilus fought alongside Isis in the early 2010s.

“This was an upward radicalisation where the son progressively ‘contaminated’ the mother,” said Bindner, who co-founded the JOS Project, which analyses the digital and media strategy of extremist groups.

“In the Bondi Beach case, we don’t yet know how it worked. It seems as if the son was involved in a network linked to Isis.”

‘Less readable’

Rodde said jihadist structures were now tending to reduce the size of cells to “very restricted groups of two or three individuals, even lone actors”.

One Western intelligence source said that made the threat “atomised” and “less organised”, allowing rapid radicalisation.

“It’s harder to work on because the structures are less readable,” they added.

Western intelligence agencies have long kept a close eye on potential recruiting grounds for Islamist extremists, such as mosques, bookstores and certain neighbourhoods - or online.

Radicalisation within a family makes the authorities’ job more difficult, said Mohammed Hafez, a specialist in Islamist movements, political militancy and violent radicalisation at the Naval Postgraduate University in Monterey, California.

“The conversations are private. They don’t need to get on Telegram, on WhatsApp or other platforms that can be observed,” said Hafez, who wrote a 2016 paper “The Ties That Bind: How Terrorists Exploit Family Bonds”.

Families, friends or work could help stop an individual being radicalised over a platform such as Telegram, but if it happens in the home “you are trapped”, he added.

“You are with that loving brother or you’re with that father or with that husband or wife. There is no walking away from that. There’s no countervailing voices because you’re trapped in that relationship.

“I suspect a lot of people will go along with a brother or a father or a husband or a wife, not because they buy the ideology or they believe in the cause but because they value the relationship.”

-Agence France-Presse