In 1997, a small-town Oregon librarian was strangled in her home — a case that went cold within months and stayed that way for over two decades. But buried inside three other seemingly unrelated murders across two states was a behavioral fingerprint so precise that one FBI criminal analyst became convinced a single mind was behind all of them, despite the fact that investigators refused to connect the dots. Tonight, we examine how the science of criminal signature evidence — and one woman's refusal to be dismissed — finally forced a reckoning.