M

Among other qualities the movie attempts to understand the relevant pathology of its time at the risk of making sense of it. I like how The Shining overlaps with the movie in terms of the toolbox used; Taxi Driver is an interesting tangent for the time where M kind of killer is no longer somebody exceptional.

Among the pathologies it seems newspapers were a mess at the time, so maybe diving into that is a lead to have some understanding of the movie context. But then modern media context is unlikely to be healthier.