As investigators struggled for weeks to find who might have committed the brutal stabbings of four University of Idaho students in the fall of 2022, they were focused on a key piece of evidence: DNA on a knife sheath that was found at the scene of the crime.

At first, they tried checking the DNA with law enforcement databases, but that did not provide a hit. They turned next to the more expansive DNA profiles available in some consumer databases in which users had consented to law enforcement possibly using their information, but that also did not lead to answers.

FBI investigators then went a step further, according to newly released testimony, comparing the DNA profile from the knife sheath with two databases that law enforcement officials are not supposed to tap: GEDmatch and MyHeritage.

It was a decision that appears to have violated key parameters of a Justice Department policy that calls for investigators to operate only in DNA databases “that provide explicit notice to their service users and the public that law enforcement may use their service sites.”

It also seems to have produced results: Days after the FBI’s investigative genetic genealogy team began working with the DNA profiles, it landed on someone who had not been on anyone’s radar: Bryan Kohberger, a doctoral student in criminology who has now been charged with the murders.

The case has shown the promise and the unregulated power of genetic technology in an era in which millions of people willingly contribute their DNA profiles to recreational databases, often to hunt for relatives. In the past, law enforcement officials would need to find a direct match between DNA at the crime scene and that of a specific suspect. Now investigators can use consumer DNA data to build family trees that can zero in on a person of interest — within certain policy limits.

While some companies have allowed users to choose whether their DNA information may be used to help criminal investigations, the decision by authorities to skirt those limits could mean that the companies’ privacy assurances are essentially meaningless.

Erin Murphy, a law professor at New York University who focuses on DNA and new policing methods, said she was surprised that the FBI might have violated rules that the federal government had spent so much time working to establish.

She was also concerned that investigators seemingly had no repercussions for doing so.

“I think what we are teaching law enforcement is that the rules have no meaning,” she said.

Steve Kramer, a former FBI lawyer who has specialized in genetic genealogy investigations, said the rules were designed as a framework, not a legal limitation. They can help guide typical investigative work, he said, but when it comes to a serious case where other investigative options are limited, such as the Idaho case, investigators may need to take additional steps.

“We’ll never know, thank God, what Bryan Kohberger would have done had he not been caught,” he said.

On the morning of Nov. 13, 2022, four University of Idaho students — Madison Mogen, 21; Kaylee Goncalves, 21; Xana Kernodle, 20; and Ethan Chapin, 20 — were found dead in an off-campus home, the victims of a vicious stabbing spree.

The police spent weeks looking for a suspect.

Behind the scenes, investigators were examining a wide range of people: classmates, people charged with prior assaults and some people with the thinnest connections to Idaho. On a knife sheath found next to two of the victims, investigators found DNA. But when they put the sample into the federal law enforcement database CODIS, there was no match.

In recent testimony from a closed-door court hearing, Idaho officials described how on Nov. 22, investigators brought the DNA sample to Othram, a company near Houston that specializes in genetic genealogy, often helping law enforcement solve decades-old cold cases by taking a modern analysis of the DNA profile. Othram began doing genetic genealogy and building a family tree, apparently following the protocols of Justice Department policy.

Kramer said the policy had been put into place after he and other investigators used genetic genealogy to solve the Golden State Killer case in 2018. In that case, investigators had used online services to identify a new suspect.

Those services were uncomfortable with the intrusion, but some, such as GEDmatch, have since allowed users to consent to having their data included as part of a DNA analysis tool that can be used by law enforcement.