"I just can't believe anyone would do something like this".
Those were the first words uttered by nursing student and volunteer Nickilynn Estologa to waiting news crews at the Boston Marathon.
It's a sentiment most people would share. The chaotic and horrifying pictures taken after the explosions in downtown Boston are like visions in a nightmare. The pavements are covered with blood; injured bystanders lying motionless or being attended by medics.
The instant response to such horror is shock, pain, empathy, anger. Why would any human choose to hurt and kill innocent people - people who were running on the streets of Boston to raise money for charitable causes, to help the sick or vulnerable in their communities or to support relatives or friends?
Our first reaction is to shake our heads in disbelief and ask the same question posed by Estologa and other volunteers who switched from massaging sore legs to desperately administering life saving treatment within a matter of minutes. How could someone do this?
But while we are reading the breaking news stories, the minute by minute coverage and the messages from friends saying they are safe and well, the most amazing stories begin to be revealed. The stories that will bring hope in years to come, when memorials are laid and the victims remembered.
Within hours, thousands of people from all around the Boston area had offered spare rooms and sofas to people who had evacuated the downtown area. A Google document created by members of the public and accessible online was full of phone numbers, addresses and offers of warm beds. Huge numbers offered to drive into the city to collect evacuees and provide comfort in the face of desolation.
Dozens of runners didn't stop running when they saw the explosions. Many went straight from the Marathon to local hospitals to give blood for life-saving transfusions, or ran towards the site of the explosion to help the injured.
Over 50 countries were represented in the Marathon. In some of the pictures you can see the flags of dozens of nations lining the end of the course. The ethos of the Boston Marathon was community, camaraderie, human endurance and caring.
That ethos was present more than ever in the actions of ordinary people after the attack. While heinous acts expose the worst of humanity, the reaction of the people of Boston exposed the best.
The same was true of the 7/7 London bombings and the 9/11 attacks. It's the stories of heroism and human decency that stick in our minds. Davinia Douglas (neè Turrell), a victim of the 7/7 London bombings, said after her recovery: "It still baffles me to this day how people can be so brutally cruel to each other. London is my home and I continue to use the Tube everyday."
This bravery and sense of loyalty to 'home' is replicated in sites of violence and terror throughout the world. In places like Badaber and Peshawar, remote villages in northwestern Pakistan, where girls' schools are frequently bombed or targeted by the Taliban, and yet teachers return after attacks to teach amid the rubble. The bravery of teachers and students in the midst of such violence is unimaginable.
The ethos behind the Boston Marathon is hugely powerful. People were running to raise money for charity, to support weary friends, to take part in an event which mixes the international and the local. The horror of what happened won't be forgotten. But neither will the response of ordinary people to appalling acts of violence, responses which show that even in the depths of absolute horror and despair, the best aspects of humanity shine through.