Her work and notes did not directly, or even indirectly, lead to the capture of the Golden State Killer. Genetic genealogy led to his capture. They uploaded his DNA profile to a DNA database, where they found several distant relatives. They then used genealogy to trace them all back to a common source, and from there created a list of possible suspects. They then used what they already knew about the Golden State Killer to eliminate possible suspects until only Joseph James DeAngelo remained. This was a shitload of work done by investigators, and Michelle McNamara had nothing to do with any of it