Stuart Trimby from Cardiff told us how he was on the last mile of the Boston Marathon when he heard two explosions.
Pictured here with his friend Emma Clatworthy Davies before the race, he said he feels "shock and sadness" at the way a positive occasion was ruined by the explosions.
You may find some of the images in the video upsetting.
More top news
Football and rugby fans the length of Wales will be starting to prepare for one of the biggest sporting weekends the country has ever seen.
Wales only need one point against Bosnia-Herzegovina to secure them a place in Euro 2016 but what do the two countries have in common?
Former Wales football manager Mark Hughes says that if Wales qualify for Euro 2016 it will be fantastic for the fans, players and the nation