The Boston Marathon is due to be held amid unprecedented security, one year after a pair of home-made pressure-cooker bombs killed three people and wounded more than 260 others.

Bostonians are shocked but resilient following this week’s bomb attack, writes John Riordan

As the FBI launched a hunt for those responsible for the Boston Marathon bombings, US President Barack Obama said: “We will find out who did this. We’ll find out why they did this. Any responsible individuals, any responsible groups, will feel the full weight of justice.”

The fatal explosions in Boston have hints of a right-wing terrorist attack rather than al Qaida-inspired extremism, according to one of the world’s leading experts on counter-terrorism.