The obvious answer to this question is that hate homicide, like other hate crimes, is motivated by a pathological antipathy, or hatred, for a group of people. Hate murderers act on this hatred by killing one or more people that they identify with the group of people they hate. This crime is, sadly, not terribly uncommon in the United States, and in murders identified as hate crimes by the Department of Justice, racial animosity is the most common specific motive. The murder of nine African American men and women at an AME Church in 2015 is a textbook example of a hate crime. The killer, Dylan Roof, was a white supremacist and hoped that his actions would lead to further outbreaks of racial violence. That no such outbreaks occurred perhaps points to a possible answer to the second part of the question--how we might prevent hate homicides. The Charleston shooting sparked widespread outrage and was identified almost immediately as a hate crime, motivated solely and explicitly by racial hatred. The murder opened up a conversation about race in South Carolina's (and indeed the nation's) past and present. So perhaps a first step to preventing these crimes is identifying them as such when they do happen--giving them the same notoriety that we do terrorist attacks, for example. They must be treated as a serious threat to public safety, and the attitudes that produce them must be publicly confronted. Ultimately, however, to end hate homicides, we have to end hate, and that is a very difficult proposition.