The murder investigation included records of Italian social clubs, draft cards, and Ellis Island immigration logs. For decades, it seemed that Lindy Sue Biechler’s killer would never be found. The 19-year-old newlywed’s stabbing death in her Lancaster County apartment in 1975 had stunned her community and shattered her family. As years passed, police kept working the case, slowly eliminating suspects as technology improved. Detectives on the scene had managed to save a sample of the killer’s DNA. But for decades it had no match in DNA databases of convicted criminals. That’s when CeCe Moore, a genetic genealogist at Parabon Nanolabs,...