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 decades-old secrets and crack the coldest of cases.

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Moore, the genetic genealogist at Parabon NanoLabs who helped identify Sinopoli as the suspect, has been a pioneer in the field since the 2000s, originally focusing on non-criminal human identification cases, such as helping adoptees find their biological families.

Even then, Moore and others knew these groundbreaking techniques could be used to help solve the most gruesome crimes.

"If you can identify someone's birth parents, if you can identify someone that's abandoned with no information, if you can identify an amnesiac, of course you would be able to identify a killer, a rapist, a Jane Doe," Moore told Fox News Digital.

The 2018 arrest of 74-year-old Joseph James DeAngelo — a former police officer known as the Golden State Killer who was responsible for at least a dozen murders and as many as 50 rapes in the 1970s and 1980s — served as a proof-of-concept for law enforcement that this new forensic science could help uncover secrets that have eluded them for decades.

"The Golden State killer arrest and identification was a watershed moment because that's what really opened people's eyes to the power of genetic genealogy on an international level," Moore said.

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The case opened the floodgates, with law enforcement agencies around the country contacting Moore and other genetic genealogists for help cracking cold cases. Since then, Moore and the team at Parabon have identified more than 200 violent criminals.

The scientists at Parabon use autosomal DNA single nucleotide polymorphisms, also known as SNPs (pronounced like "snips"), to identify possible distant relatives of an unknown subject by comparing that person's DNA sample to hundreds of thousands of others in a public genetic database, such as GEDmatch or FamilyTreeDNA.

From there, Moore and her team will reverse engineer the unknown person's family tree in an effort to identify that subject using traditional genealogy.

"I've got to figure out: who is this match, who are their parents, and build that family tree," Moore said.

"That sometimes means reading obituaries, reading newspaper articles, looking at social media, figuring out who these people's parents are and then their grandparents. Once I get far enough back, I can start using those traditional genealogical records that you might find on Ancestry.com or on Familysearch.org, but there's a lot of creativity that has to go into it."

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The DNA Doe Project, which focuses on identifying Jane and John Does, sometimes is able to use a voluntary target uploader — a potential relative of a missing person who uploads their DNA sample from a commercial site like 23andMe to a public database like GEDmatch to help investigators build out a clearer family tree.

"These people have family and friends and loved ones that are missing, so usually, when it comes to our mission, people are really motivated to help, and they're happy to upload to GEDmatch," DNA Doe Project team leader Cairenn Binder told Fox News Digital.

Just two weeks before the Golden State Killer was arrested by law enforcement in California, the DNA Doe Project successfully identified the "Buckskin Girl" as Marcia King, a 21-year-old woman who was murdered in April 1981.

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It was one of the first victims ever identified using genetic genealogy. Since then, detectives from the Miami County Sheriff's Office in Ohio have worked to reconstruct what led up to her murder more than 40 years ago with the hopes of identifying a suspect.

"If you don't know who somebody is, how do you know who killed them?" Binder said. "The vast majority of people who are murdered are killed by people that know them, that are in their friends and family. So, if you have a homicide victim and you don't have their identification, then that doesn't give law enforcement a good place to start with investigating their killing."

While genetic genealogy has proved to be a remarkable advancement in finding long searched for answers, privacy advocates have taken issue with its potential for civil rights violations.

"Now is the time for legislators, the courts and law enforcement to ensure that the benefits of genetic-science technology don’t come at the cost of our privacy rights," Vera Eidelman, a staff attorney with the ACLU’s Speech, Privacy, and Technology Project, wrote after the Golden State Killer was arrested.

"Blockbuster investigations, as gratifying as they are, shouldn’t obscure the very real dangers of government access to sensitive information."

The most popular at-home genetic testing companies do not allow genetic genealogists to access their databases, and law enforcement can only pull a DNA profile with a warrant.

These privacy concerns are legitimate and have been at the forefront of genetic genealogists' minds since the beginning of the booming field, Moore said.

"I, at the time, was hesitant to start doing this work because I wanted to make sure it was something positive and that people didn't see it as a betrayal or a privacy issue," Moore said.

"I've had hundreds of people come to me, thousands of people probably, entrust me with their family mysteries, with their secrets," she continued. "I have seen how sensitive people are about their DNA, understandably, right? It's something that is so personal to us."