(NewsNation) — Idaho killing suspect Bryan Kohberger is behind bars after DNA from the crime scene was linked to DNA from trash at his parent’s home. But how do investigators use genetic evidence to find a suspect?

DNA first started being used in the 1980s. The nation’s first conviction came when Tommie Lee Andrews was sent to prison for rape after investigators used a lab paternity test in the case.

Typically, law enforcement officials use a system called CODIS, run by the FBI, which indexes DNA samples taken from crime scenes and those convicted of crimes, though states may also have their own databases.

But in 2018, police turned to a new technique in the case of the Golden State Killer. The suspect, a police officer, had left DNA at the scenes of his crimes for decades, but he wasn’t in the system. So police turned to genetic genealogy websites, where people send in samples of their DNA to look for relatives, looking for a connection to relatives.

They found it, and Joseph D’Angelo was arrested and pled guilty, even confessing to additional crimes.

Denver’s former District Attorney Mitch Morrisey co-founded United Data Connect after spending more than three decades as a prosecutor. He credits investigative genealogy with an explosion of arrests in cold cases.

“We don’t solve the case, we provide them with a name of a person that most likely left the DNA,” he said.

Investigators say the key in this case was a sample of DNA from the crime scene being compared to trash at the Kohberger’s Pennsylvania home. They used DNA belonging to Kohberger’s father to show a familial link, which led to Kohberger’s arrest.

Genetic genealogist CeCe Moore told NewsNation she thinks there’s probably more to the story than that, but it’s likely investigative genealogy played a role.

“They don’t have to include everything in the affidavit and genetic genealogy should not be used for the basis of an arrest,” Moore said.

It can be used to vet tips, like the one about the white car seen near the crime scene, she said. Police would have taken trash from the Kohberger home and used DNA from that to essentially perform a paternity test against DNA taken from the knife sheath found at the crime scene.

Kohberger is accused of killing four Idaho college students, Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin. All four were stabbed as they slept and as weeks went by with no suspect speculation and rumors ran rampant online.

The first break in the case came as police began searching for a white Hyundai Elantra. That car, along with forensic evidence, led to Kohberger’s arrest.

Moore said technology has increased in sensitivity over the years, allowing investigators to recover DNA even in the absence of blood. Kohberger’s DNA could have been left at the scene in a number of ways, she said, including shed skin cells or hair.

That makes it easier to for police to collect DNA samples from unexpected sources.

“I’ve seen police officers bussed tables in pizza restaurants, and gotten saliva off of pizza and off of forks and that kind of thing,” Morrisey said.

“We know from the witness statement that at least his eyebrows were showing, and it sounds like his hair wasn’t even covered. So he may have left hair behind as well, which also contains DNA,” she said.

Moore said the science of investigative genealogy has come a long way, and cases can be cracked in unusual ways.

Take the case of Nancy Anderson, solved 50 years after she was murdered in Honolulu. Well-preserved DNA evidence was re-tested using current technology and Moore built an advanced family tree, including distant cousins, to eventually locale Tudor Chirila Jr., a retired deputy attorney general in Nevada. Similar to the Idaho case, police got a DNA sample from Chirila’s son before making the arrest.

Moore cautions that investigative genealogy is a tool and can’t be the sole basis of an arrest.

“Investigative genetic genealogy, even though it’s a more advanced technology, it is simply a lead generator, it is a tip and no arrest can be made based on that information. So they have to treat it the same as if I call the tip into Crimestoppers,” she said.

Just last month, DNA helped reunite Melissa Highsmith with her birth family after she was kidnapped 51 years ago.

Genealogists say only two companies, Family Tree and GEDMatch, share DNA profiles with law enforcement and users must opt-in.

“It’s a big misconception out there that we’re able to use Ancestry DNA and 23andme, they have over 40 million people in them, if we could use those databases, these cases would take an hour,” Moore said.

In four years, this technique has cracked around 400 cases, most of them cold cases with vulnerable victims.

“In cases where DNA is significant, 90% of the victims are women, the 10% that are left, about 9.5 are kids. So this is a science that we then add genealogy to when DNA hasn’t been able to give us an answer that solves crimes, and violent crimes against women and children,” Morrissey said.

Now there is a push to find new killers using genealogy.

“There is no reason we need to have serial killers, Ted Bundy types serial rapists because we can identify them after the first violent crime,” Moore said.

While an arrest has been made, Moore said the search for forensic evidence isn’t over as both prosecution and defense teams will be scouring the crime scene evidence for information that can be used in court.

“There’s been a lot of work on that crime scene already, gathering any possible physical evidence to the prosecution’s case, try to support their case, or in the defense’s case, to try to find somebody else’s DNA that they can try to pin this crime on,” Moore said.

Tune into the NewsNation Special Report: Idaho Murder Mystery on Sunday at 9 PM EST/8 PM CST.