On the 22nd of April, 1992 a series of huge explosions ripped through the Mexican city of Guadalajara, opening up a trench almost eight kilometres (or five miles) in length. The destruction was absolute – hundreds were killed, thousands injured, and vast tracts of the city damaged beyond recognition. As shocked survivors began digging through the rubble, the question remained: what could possibly have caused this kind of devastation on such an enormous scale?