(Newser) – The man police say is Arizona's "Canal Killer," who killed two women—beheading one of them—in the early 1990s, was caught in large part because some relative of his somewhere submitted their DNA to one of those public genealogy databases, the Arizona Republic reports. Suspect Bryan Miller was arrested in 2015 after police matched his DNA, collected surreptitiously, with DNA from the crime scenes. But it's only now being revealed how they knew to sneak some DNA off of Miller. It starts with genealogist Colleen Fitzpatrick, who met investigators at a human-identification conference in 2014. One of the topics of the conference: How to figure out an unknown person's last name by studying their Y chromosome.

While redacted police emails make it unclear exactly how Fitzpatrick narrowed the Canal Killer down to someone with the last name Miller, one expert says it's probable she compared the Y-STR—a genetic "stutter" that passes unchanged from father to son through generations—from crime scene DNA with Y-STRs in public genealogy databases like Ancestry.com or Family Tree DNA, giving her the surname "Miller." Fortunately, police just happened to have a Miller on their "extensive list of candidates." These public genealogy databases are usually used by people trying to find their birth parents or see if they're related; there's "little precedent in the world of criminal justice." Read the full story to find out how forensic genealogy can be used by law enforcement in the future and the privacy concerns that brings up. (Read more genealogy stories.)

