Amid the anarchy of post-Revolution Libya, seven ruthless brothers from an obscure background gradually took over their home town near Tripoli. They're accused of murdering entire families to instill fear and to build power and wealth. They created their own militia which threw in its lot, at different times, with various forces in Libya's ongoing conflict. And they grew rich by levying taxes on the human and fuel traffickers crossing their territory. Now, the full horror of their reign of terror is being exposed: since they were driven out in June, more and more mass graves are being discovered. The Libyan authorities - and the International Criminal Court - are investigating what happened. But the four surviving Kani brothers have fled. Will they ever face justice? And what does their story tell us about why the 2011 overthrow of Colonel Gaddafi brought not democracy, but chaos, to Libya? Tim Whewell reports.