I have already posted on this.
Any physical difference from the norm can be seized upon and used against the individuals who can do nothing about them. These individuals, deviant because of a physical characteristic (in this case, one they do not control) are then subjected to dehumanization and violence, used as scapegoats and otherwise see their capacity for social participation drastically limited.
Case on point, via the BBC.
In this case, the combination of social stigma with traditional beliefs and possibilities of profits on both side of the transaction (witchdoctors and patients) and the inevitable police corruption create a deadly situation for many albinos in that region.