4 ideas
From 1974 to 1986 one man committed at least 13 murders and about 50 rapes across California under separate regional names: the Visalia Ransacker, the East Area Rapist, and the Original Night Stalker. Michelle McNamara coined the name 'Golden State Killer' and spent years investigating him, then died in 2016 with her book unfinished.
When crimes fall across different police agencies, each agency keeps its own files, its own suspect names and its own local label, so no one sees the whole pattern. For decades the Sacramento rapes and the Southern California murders looked like separate offenders, and DNA only linked them in 2001. Giving the offender one unified name was an investigative act, because it forced the scattered cases to be seen as one case.
A cold case can be solved decades later without new witnesses if the physical evidence was kept long enough for forensic methods to catch up. The key decision is often made years earlier by whoever chooses not to discard old evidence.
Treating the hunter's fixation as the story reveals what a long investigation costs the person running it: insomnia, compulsive rechecking of details, and a mind that keeps living inside other people's worst nights. McNamara's drive to put a face to an anonymous predator produced real leads and public pressure. It also consumed her, and her life ran alongside the case until it ended before the answer came.