The Guardian investigates the causes behind the murder of Tristan Voorspuy, a former British army officer shot on his ranch by nomadic herders in March. The central Kenyan county of Laikipia has become the epicentre of a bloody conflict between pastoralists from the north and farmers whose land they have invaded. A severe drought aggravated by climate change is partly to blame, but so is political manoeuvering before general elections on 8 August.