http://abc7news.com/dna-that-cracked-golden-state-killer-cas... This article states that the main DNA sites and Ancestry.com didn't release the information, so I'm curious about where it came from as well. Though it does say they'll comply with 'valid legal requests' it also says they weren't contacted.
There are public databases that allow you to specify your DNA haploids and will show you matches. I linked to one in another comment. They likely used that specific site, although there are other sites that provide the same functionality.