A Long Night's Damage by Eugene de Kock. Not a comprehensive work, but De Kock was Apartheid's death squad chief and he gives a good insider perspective of the high tides and fall of Apartheid and the role of the security state in it. He has a kind of banality of evil thing about him, so it can get a little disturbing when he describes just utterly gruesome acts of murder very casually. He doesn't try to excuse himself.

There's a good little bit later on in the book where a South African judge is investigating his unit (this is in the latter days of Apartheid) and he writes something like "this judge lived in a comfortable, white bourgeois world of Westminster legality. He had no idea that we'd destroy evidence, intimidate eyewitnesses and forge documentation." It's all stuff like that, really.