" Scrolling through the rest of the 3,500 documents in Michelle’s hard drive, one comes upon a file titled “RecentDNAresults,” which features the EAR’s Y-STR markers (short tandem repeats on the Y chromosome that establish male-line ancestry), including the elusive rare PGM marker. Having the Golden State Killer’s DNA was always the one ace up this investigation’s sleeve. But a killer’s DNA is only as good as the databases we can compare it to. There was no match in CODIS. And there was no match in the California penal system’s Y-STR database. If the killer’s father, brothers, or uncles had been convicted of a felony in the past sixteen years, an alert would have gone to Paul Holes or Erika Hutchcraft (the current lead investigator in Orange County). They would have looked into the man’s family, zeroed in on a member who was in the area of the crimes, and launched an investigation. But they had nothing. There are public databases that the DNA profile could be used to match, filled not with convicted criminals but with genealogical buffs. You can enter the STR markers on the Y chromosome of the killer into these public databases and try to find a match, or at least a surname that could help you with the search. "

― Michelle McNamara , I'll Be Gone in the Dark: One Woman's Obsessive Search for the Golden State Killer