The award was for their article 'A true horror story: The abuse of teenage boys in a detention centre.'
The piece, which featured in the Guardian Weekend magazine, won in the Magazines - Newspaper Supplements category.
The winners were announced at a ceremony at the British Film Institute in central London on Wednesday 12 June 2013. The awards recognise excellence in human rights reporting and acknowledge journalism's significant contribution to the public's awareness and understanding of human rights issues.
Click here for more information and for a full list of winners.
