The disappearance of 13-year old Yara Gambirasio became known as the murder that obsessed Italy for years. Her killer left behind DNA on her clothing, but Italian police could only identify him as “Unknown 1”.

But, the police didn’t know who “Unknown 1” was. His DNA didn’t match any sample in local or national DNA databases. It was as if their suspect didn’t even exist.

How could police and forensic scientists use genealogy, DNA testing, and old-fashion detective work to finally track down their suspect, “Unknown 1”?