Serial killer Aileen Wuornos came to my attention when Charlize Theron played her in Patty Jenkins's "Monster". It turned out that Wuornos had been famous for over a decade before then. Nick Broomfield's "Aileen Wuornos: The Selling of a Serial Killer" focuses on Wuornos's arrest and prosecution.
The topics noted by the documentary are that Wuornos had a dismal childhood (resulting in her proclivity towards violence); and that during the trial, a number of people tried to enrich themselves from the publicity. Basically, there were no good guys; the documentary doesn't heroify Wuornos, but also shows what opportunists everyone else was.
Broomfield made a second documentary about Aileen Wuornos, but I haven't seen that one, only this one and "Monster" (it turns out that there was also a 1992 movie about Wuornos starring Jean Smart). The point is that Wuornos is a clear example of how a harsh upbringing can turn someone into a sadist - that is, a screwed-up society breeds screwed-up people* - and how people will then want to profit from it. Definitely worth seeing.
*That was also one of the points made in "A Clockwork Orange".