The Rwandan genocide of 1994 occurred due to widespread complicity. I will argue that complicity can be the basis for legal liability, even for criminal liability, if two conditions are met. First, the person's actions or inactions must be causally efficacious at least in the sense that had the person not committed these actions or inactions the harm would have been made significantly less likely to occur. Second, the person must know that her actions or inactions risk contributing to a harmful enterprise, and must intend that these actions or inactions risk making this contribution. But it is not part of this analysis that the defendant must intend the harmful result. I explore the boundaries between legal and moral complicity and end with a discussion of how the analysis defended in the paper affects such questions as how many people in Rwanda should be prosecuted for the genocide which occurred due to widespread complicity.