I have met the assassins, too; men like Jose Antonio from Ciudad Juarez, probably the most murderous city on the planet – just seven miles from the border with the US. Jose stands at just five feet six and has chocolate coloured skin, earning the nickname "frijol" or bean. He has a mop of black curly hair and bad acne, like many 17-year-olds. But despite his harmless demeanour, he has seen more killings than many soldiers serving in Iraq and Afghanistan.