A tip off from a former secret police officer have led residents in the rebel-held town of Derna in eastern Libya to unravel secrets that were hidden by Muammar Gaddafi's regime for decades.

A mass grave has been discovered in the area, and forensic doctors have found pieces of bone and clothing.

They fear there are as many as seven people buried there.

Al Jazeera's Sue Turton reports from Derna.