Three weeks ago a remarkable caravan of vehicles arrived at the Mexican town of Reynosa, just across the border from Hidalgo, Texas. It left the northern border of Nicaragua on 12 October, carrying the relatives of migrants who made the journey north to cross illegally into the United States, but vanished along the way. The caravan, which finished its journey through Central America this weekend, was trying to draw attention to their disappearance and – if possible – find them.