When police and soldiers in Sri Lanka set out on the trail of the attackers who killed more than 350 people in a series of bombings on Easter Sunday, they did not expect to find themselves in Dematagoda, one of the wealthiest neighbourhoods in Colombo.

Within 90 minutes of the attack, as hospitals struggled to cope with the huge number of casualties, the security forces were closing in on a three-storey house with a BMW parked outside.

Two brothers lived there with their families: 38-year-old Inshaf Ibrahim, a copper factory owner, and Ilham, 36. Their father, Mohamed Yusuf Ibrahim, one of the most successful businesspeople in the island nation’s Muslim community, made a fortune exporting spices. The two brothers were also involved in the jewellery trade. They were both among the attackers.

When police moved in, there was another blast. It is unclear whether the top floors were wired with explosives or if the elder brother’s wife, Fatima, had set them off. The couple’s three children were instantly killed.

On Thursday, police confirmed that Mohamed Yusuf Ibrahim had been detained.

“They seemed like good people,” a neighbour told reporters from her rundown home opposite the Ibrahim family residence in the capital.

Facebook Twitter Pinterest An explosion ripped through the house when police raided it after the attacks. Photograph: MA Pushpa Kumara/EPA

In an interview with CNN, Sri Lanka’s prime minister, Ranil Wickremesinghe, said the suspected bombers were upper and middle class, and were well educated abroad, a profile he described as “surprising.”

His surprise was widely shared. In the Sri Lanka, the wider region and beyond, many still find it very difficult to understand how those with comfortable lives can be drawn into extremism, and kill themselves and hundreds of innocent people.

The question has been asked many times before. In Europe, it became an issue in the 1970s when relatively well-off young men and women in Germany, Japan, Italy or the US began to engage in violent activism. With the spread of suicide tactics in the 1980s and early 1990s, it seemed more perplexing than ever.

Then came a new wave of Islamic militancy, with attacks of unprecedented lethality. None of the men who flew planes into the World Trade Center in New York in 2001 faced economic hardship. The leader of their organisation, Osama bin Laden, was the son of a construction tycoon.

One of the Easter Sunday bombers attended Kingston University in south-west London from 2006-07, where he studied aeronautical engineering, and then went on to study in Australia. From a wealthy tea trading family based near the central city of Kandy, he had attended top international schools – as had other bombers, it appears.

There are many examples of terrorists with good educational qualifications among Islamic militants. The current leader of al-Qaida, Ayman al-Zawahiri, is a qualified paediatrician, while two-thirds of the 9/11 attackers had degrees. One plot in Britain in 2007 was almost entirely composed by highly qualified medical personnel.

Facebook Twitter Pinterest The al-Qaida leader, Ayman al-Zawahiri. Photograph: AFP/Getty Images

A group of Bangladeshis linked to Islamic State that attacked a bakery favoured by westerners in Dhaka in 2016, killing 20 hostages, share a similar profile to the Sri Lankan bombers. Almost all were from wealthy, highly educated backgrounds.

Isis has claimed Sunday’s bombings – its most lethal attack since its emergence five years ago. The group’s leadership has a rather different composition. Many are religious clerics, or former Ba’ath party officials. But many of the volunteers who travelled to Syria and Iraq from countries such as Egypt or Tunisia were from comfortable backgrounds, too, as were many who travelled from the UK.

Muslims in hiding in Sri Lanka as tensions rise after bombings Read more

However, on close inspection, many of the terrorists who went to university never finished their degrees. Others earned qualifications from institutions with dubious or limited academic credibility; many British extremists fall into this category.

Mohammed Zahran Hashim, the rural Sri Lankan preacher who is thought to have been the leader of the Easter bombing attackers and was in touch with Isis overseas, had limited wealth and only a rudimentary religious education.

Both al-Qaida and Isis have attracted large numbers of footsoldiers from backgrounds that are marginal in diverse ways. This is true in the Middle East and south Asia, where minor tribal leaders, out of work craftsmen, smugglers, former militia members, minor government officials, and poor farmers’ children sent to free religious schools have all been drawn to Islamic militant ideologies.

In Europe, many of the men who carried out recent terrorist attacks in France and Belgium were petty criminals, living on the economic margins.

Taken together, this teaches us that neither education nor economics can help explain any one individual’s violent activism. The literature on radicalisation that has been produced since 2001 has yet to pinpoint a cause, and few experts think there might be one.

Instead there are many factors that are seen as creating a risk of radicalisation. When they combine, the risk becomes a clear and present danger. Terrorism, abhorrent though it may be, is a social activity. Ideas spread and are reinforced among peers, married couples, old schoolfriends and families. These ideas are simple. They explain complex events, identities and histories through a rudimentary and binary narrative. Neither education nor wealth is proof against them, and nor is poverty or ignorance.