Having been a toddler when DeSalvo--well it was DeSalvo--was inhabiting his Measuring Man, Green Man and finally Strangler personas, and living just a half mile from him (and also being intimately acquainted with the location (in Belmont) used for Loretta's neighborhood and the Cambridge police station), I was really looking forward to this film, since the full subject really hasn't been treated dramatically, notwithstanding the 1968 Strangler movie featuring Tony Curtis. Alas, this noirish crime/reporter drama falls short of its subject, including even the story-within-story of the two "girl" reporters who largely drove the investigation at its early stages. The case has so many threads, all seeming touched on in the film, but none satisfactorily developed. It might have been done more fully in a season of one-hour episodes, perhaps loosely corresponding to each murder and subsequent developments. At least, Loretta McLaughlin and Jean Cole get more deserved recognition, albeit posthumously, for their intrepid and implacable reporting.
There's a couple of confected scenes or plot twists (the movie is only "inspired by" true events), but these aren't obviously improbable (well maybe one is) to someone unfamiliar with the case. I agree that the film suffers a bit from the conspiracists' take on whether DeSalvo really committed all (or any) of the murders, which absorbs the last quarter of the film. Finally, the cinematography is a bit overboard on the dark and dreary: even the newsroom is dark; one wonders how the staff could see to write.