In Focus: How is the act of genocide defined and can it be prevented?

Rwanda is celebrating its Independence Day - marking the end of the genocide in 1994. During that brutal period, around 800,000 people, or a tenth of its population, were killed by Hutu extremists. Meanwhile on another continent, the people of Srebenica are remembering the massacre of 8,000 Muslim men and boys by Bosnian Serb forces. But how is the act of genocide defined? And more importantly, can it be prevented?