I have seen this article or headline of it over the internet but here is an interesting BBC report which mentions the arrest in the Golden State Killer case:
I gave my DNA away. Can I get it back?
Here is part of the article:
In April last year, it was revealed that US police uploaded DNA they suspected of belonging to a man thought to have committed multiple rapes, murders and burglaries across California, to GEDMatch, a free online database where anyone can share their genetic code in order to search for relatives who have also submitted theirs.
From this, police were able to create a complex family tree with the details of around 1,000 people, which led eventually to the third and fourth cousins of Joseph James DeAngelo, who was arrested and charged with the crimes.
None of those whose data was compiled had given prior consent for their data to be used in a murder enquiry.