'We want to know where they are': How the discovery of a mass grave sparked uproar over the missing in Mexico

When they got to the deserted ranch, the volunteer searchers found watches and dirty football jerseys, an applied psychology book and a copy of the Bible. There was even a heart-shaped keychain containing a cut-out photo of a young woman.

But one set of artefacts was particularly chilling: the sight of hundreds of dust-caked shoes, thought to be discarded by victims who were murdered and incinerated in nearby ovens. READ MORE from Al Jazeera