The Green River Killer — who is believed to have killed at least 49 women killed in Seattle between 1982 and 1984 — baffled police for almost two decades, but a suspect finally was arrested last year.
Last December, Gary Leon Ridgway pleaded not guilty to killing four women. Prosecutors expect to make the other Green River deaths an issue in the trial, which is not expected to begin for another year.
In the Green River case and other longstanding serial killer investigations, DNA evidence proved to be the key.
In a few rare instances, serial killers have simply turned themselves in.
In 1998, Wayne Adam Ford walked into the Humboldt County Sheriff's Department in Northern California and told deputies he'd killed four women. He then took out a plastic bag with a human body part inside.
But in many cases, it was a simply good luck or a key mistake that led police to the attacker.
Charles Ng was convicted 1999 of 11 murders in Northern California. The killings took place in 1984 and 1985, but investigators found Ng only after his partner in crime, Leonard Lake, was caught shoplifting and poisoned himself to death in police custody.
"It's often just a matter of luck. It really is," says Harold Schechter, a literature professor at Queens College in New York, who has written extensively about serial killers.