Using logistic regression on the 36 democracies studied in Lijphart's Patterns of Democracy, we find statistically significant correlations between the index of consensus democracy and a higher incidence of fatal domestic terror incidents in the period 1985 -2010. We further find that the risk of fatal terrorist attacks is almost six times higher in majoritarian democracies than in their consensus counterparts, and that this indicator is stronger than factors such as economic development and a large youth population and levels of urbanisation. set off bombs in central London on 7 July 2005. In the aftermath of the atrocities, one question was asked: why did citizens kill fellow citizens in terror attacks? This question is the focus of this paper. Excluding international terrorism (foreigners perpetrating acts against citizens of another country, such as the 9/11 attacks), the paper seeks to understand the factors behind mass atrocities perpetrated by domestic -or 'home grown' -terrorists. The main hypothesis of the paper is a refinement of the thesis that consensus democracies are less likely to suffer terrorist attacks as marginalised groups of citizens are more likely to influence political decisions in countries with coalition governments, multiparty systems and the like. BACKGROUND