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.
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Runners looking to compete in the Newport half marathon have been disappointed again after it was cancelled due to weather warnings.
Very cold and windy. Some sunny breaks but plenty of snow showers feeding in the from the east.