The bombs that killed three people and injured more than 200 others at the Boston Marathon in the US last month were set off by two brothers, one disenchanted with America and the other apparently following his lead.
Tamerlan and Dzhokhar Tsarnaev had emigrated to the US from Dagestan, Russia, in 2002 but had failed to integrate, although Dzhokhar, who was more religiously moderate, had seemed happy and well adjusted at university.
Tamerlan, 26, died in a shoot-out days after the bombing. His younger brother, 19, has been charged with using a weapon of mass destruction and is scheduled to appear in court on 30 May. The crime carries the death penalty. Although this was abolished in the state of Massachusetts almost 30 years ago, it still exists in the federal courts where Dzhokhar will be tried.
The laws governing the trial of a terrorist differ from those in a civilian court, and there was some debate over whether Dzhokhar should be tried as an "enemy combatant", which would have limited his human rights. (He would not, for example, have been permitted access to a lawyer.) The state eventually decided to try him as a US citizen.
The Federal Bureau of Investigation defines terrorism as "the unlawful use of force and violence ... in furtherance of political or social objectives".
But what do we know of the brothers' motives? And what does this atrocity tell us about modern terrorism? Tamerlan had been on the US government's Terrorist Identities Datamart Environment list for 18 months but had not been deemed a serious threat.
The brothers appear to have acted alone, without the support of any outside extremist groups, prompting concern about what authorities say is a growing trend of "lone wolf" terrorist attacks. Perpetrators may sympathise with the ideology of a particular organisation yet have no direct contact with them, making it difficult for authorities - more used to hunting cells, or groups, of terrorists - to detect them as a threat.
Experts tracking Tamerlan's path to Islamic fundamentalist extremism say that he appears to have "self- radicalised", using YouTube videos and information found on the internet.
Yet some claim that self-radicalisation is not a new phenomenon. Marc Sageman, a former Central Intelligence Agency operations officer who now acts as a political violence consultant to the US government, says: "The huge majority - 90 per cent - of plots in the West since the 1990s have come from people who decide to do it on their own and who don't have links with the outside."
A recent, high-profile case of "lone wolf" terrorism was that of Anders Breivik, who murdered 77 people, mainly adolescents, in Norway in 2011 when he bombed government buildings in Oslo and opened fire on a Labour Party youth camp. He later claimed that his actions were a protest against mass immigration.
- How would students define terrorism?
- Is violent protest ever justified? Ask students to explain their reasoning.
- What is an acceptable and democratic way of monitoring potential terrorist threats?
- What degree of invasion of privacy is justified to keep us safe? Debate.
- How should the press report terrorist activities? What kind of language should be avoided so as not to encourage religious hatred?