The Sacremento mass murder suspect was found, via GedMatch, which is not a testing firm. It classifies samples sent t them by individuals, obtained from the testing companies.
Example: You get your DNA tested by Ancestry. Ancestry says your ancestors came from Ireland and Italy. Ancestry tell you about some close cousin matches, too.
You in turn can take thesample results obtained from Ancestry, and upload the data to GedMatch.
GedMatch in turn may give alternate interpretations about origins, and some additional cousin matches.
I have yet to get cousin matches from GedMatch, but my sister has had them, from Ancestry. Solid. every time.
DNA science is very solid.