Lots of people in the DNA databases are relatives to someone who lived in Sacramento.
I wonder how many close DNA matches did they find, and eliminate because there was no viable relative who could be a suspect?
DNA is useful, but factoring up the probabilities in this case is not easy. Good luck trying to explain that math to a jury.
The lead came from the police searching through DNA databases which identified some set of relatives who were suspicious, but they later obtained the DNA from the suspect himself which was an exact match to what was gathered from crime scenes.
But yes, good luck explaining that math to a jury.
Previous to the East Area Rapist, the suspect lived 200 miles away, in the next town over, when the Visalia Ransacker terrorized the neighborhood with over 100 bizarre break-ins. He would break into women's houses and ransack them and only take things of little value while using leaving things of value in sight.
It has long been suspected for a long time the Visalia Ransacker moved to Sacramento to become the East Area Rapist, but there's no conclusive proof (at least yet). There was no DNA taken in the Ransacker cases. The MO and suspect were very similar, it seemed that the East Area Rapist was an escalation of the Ransacker's activities.
The suspect just happened to leave the Visalia area and move to the Sacramento area at exactly the same time the Visalia Ransacker stopped his criminal spree and the East Area Rapist started his in Sacramento.
THEN the suspect was fired from the police force at exactly the same time the East Area Rapist moved his location over 600 miles away from Northern California to Southern California. It's not currently known (to the public at least) where the suspect's whereabouts were from the time he was fired from the police force (in 1979 IIRC) and from the time he took a job at Save Mart back in the Sacramento area in the early 90s.
The crimes in Northern California were conclusively proven to the crimes in Southern California through DNA evidence, unlike the Visalia Ransacker crimes.
There's more... The East Area Rapist mentioned the name Bonnie in one of his attacks http://www.coldcase-earons.com/36.php "After the rape, (HAP: he laid his head on the pillow next to her) and began sobbing "I hate you. I hate you. I hate you Bonnie." (HAP: The victim was not certain that he was saying "Bonnie," but that's what it sounded like)." The suspect, at one point in his life, was engaged to a woman named Bonnie. Bonnie Jean Colwell.