On the evening of Dec. 5, 1975, Lindy Sue Biechler’s aunt and uncle returned home to find their 19-year-old niece with a knife sticking out of her neck and signs of a struggle in the blood-splattered entrance way of the house in Manor Township, Pennsylvania.

Investigators combed through the grisly scene and continued re-examining the evidence for decades to no avail. Male DNA was obtained from Biechler’s underwear in 1997, but investigators didn’t receive a hit when they submitted it to the nationwide law enforcement database, CODIS.

In 2019, the Lancaster County District Attorney’s Cold Case unit enlisted the help of CeCe Moore, the chief genetic genealogist at Parabon NanoLabs, which used cutting-edge DNA analysis and traditional genealogy to identify 68-year-old David Sinopoli as the suspect.

In February 2022, investigators stealthily obtained fresh DNA from a coffee cup that Sinopoli threw into the trash as he traveled to Philadelphia International Airport.

That DNA was compared to blood taken from the victim’s pantyhose, which came back as a match in June, and Sinopoli was arrested at his home the next month in Lancaster, Pennsylvania. He is now facing criminal homicide charges.

After nearly five decades, Biechler’s family is starting to receive closure thanks to a burgeoning new field of forensic science called investigative genetic genealogy, which combines cutting-edge DNA analysis and traditional genealogy to uncover…