Professor Jon Cole is part of the Tactical Decision Making Research Group at the University of Liverpool’s Department of Psychological Sciences
“The radicalisation of individuals like those thought to be behind the Boston bomb is always unique, but there are also recurrent themes that allow us to understand how young men become terrorists.
“At Liverpool we have examined open source intelligence on over 300 convicted terrorists and identified a number of common characteristics – some of which are present in this case – such as cultural isolation, isolation from family, risk-taking behaviours, a sudden change in religious practice and travel to conflict zones.
“It is highly likely that these characteristics made these two young men vulnerable to the ideology that drove their attack.
“As the brothers were Chechens, talk has already turned to the role of the ongoing insurgency in the Northern Caucasus region, but so far there is no evidence that either brother was involved in that insurgency.
“It is much more likely that they are an example of what is known as ‘leaderless resistance’, where individuals and groups are inspired by an ideology to commit acts of terror in support of it.
“If this is the case then it is highly likely that most of the radicalisation occurred online without either brother ever having physically met another terrorist.
“It is increasingly common for vulnerable young people to encounter violent extremist ideology online and to associate with violent extremist organisations on social media. So far there is little evidence of such links with Dzhokhar, as his social media pages were quickly the subject of public scrutiny.
“It remains to be seen what will be found when the online behaviour of both brothers is made public. However, with so many young people using social media and posting inappropriate material on there it is not difficult to imagine that one or both of them revealed their radicalisation online.
“Once we know why the Tsarnaev brothers became terrorists there will be a need to learn the lessons and prevent it happening again.
Learning from the UK’s mistakes
“This process will be similar to that observed in the wake of the July bombings in the UK. The interesting question is whether the US will learn from the mistakes of the UK in this process.
“The key to preventing these attacks is to identify and intervene with vulnerable young people before they encounter and are exploited by ideologues and recruiters.
“As there are easily identifiable behaviours that suggest radicalisation is taking place and there are known vulnerabilities, this is a potentially achievable goal.
“The real question is whether society is willing to interfere with the individuals’ right to political freedom in the same way that it does with their unhealthy behaviour.”