BOISE, Idaho — The 19-page probable cause affidavit resulting from the investigation into the quadruple homicide of University of Idaho students in Moscow featured a slew of new or elaborated-upon information, including the fact that a knife sheath was left at the crime scene.
Investigators said they found DNA evidence on that sheath that eventually helped lead them to a suspect, Bryan C. Kohberger, who was arrested Dec. 30 at his family’s home in Pennsylvania.
DNA comparisons are often not indisputable, but they remain significant pieces of evidence in investigations and at trials. But how do police and lab analysts use genetic evidence, what are the forms of testing, and what are the pros and cons of DNA evidence?
The Idaho Statesman interviewed a pair of experts with experience and knowledge of DNA and genealogy in criminal cases to speak in general about their usage, not specifically about the court case in Moscow. They laid out the benefits while also discussing the challenges surrounding scientific evidence.
DNA in the Kohberger case
Kohberger, who was a Washington State University graduate student, has been charged with four counts of first-degree murder in the deaths of University of Idaho students Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin.
According to the probable cause affidavit, DNA was taken from the knife sheath and sent to the Idaho State Lab. Trash obtained from the house in Pennsylvania where Kohberger was arrested — he had been staying at his parents’ house since driving home from Pullman, Washington, in mid-December — was also sent to the lab for DNA testing.
When comparing the DNA found on the sheath to the DNA from the trash, test results “identified a male as not being excluded as the biological father” of the suspect. More specifically, “at least 99.9998% of the male population would be expected to be excluded from the possibility of being the suspect’s biological father,” investigators wrote in the affidavit.
Latah County Magistrate Judge Megan Marshall issued a nondissemination order in the case prohibiting any communication from those involved with the public or media, so getting answers to more detailed questions about the DNA evidence is not possible at this time.
The methods of testing DNA
There are three commonly used methodologies for testing DNA, Greg Hampikian told the Statesman. Hampikian is the director of the Idaho Innocence Project at Boise State University.
The most common method is Short Tandem Repeats, which takes short sequences of DNA that repeat continuously. There is also a method called YSTRs that uses the same process but focuses specifically on the Y chromosome, which is found only in males.
Hampikian and the Idaho Innocence Project used this latter method to gain the freedom of Christopher Tapp, who was wrongfully convicted in the rape and killing of Angie Dodge in Idaho Falls. The group used DNA found at the scene of the crime committed in 1996 and used YSTRs to determine the culprit could not have been Tapp. He was exonerated in 2019.
But neither of those methods is viable if you’re looking for a genealogical connection, according to Hampikian. Genetic genealogy uses DNA to determine the familial links between individuals.
“Geneticists are able to, by getting a paternal sample, they’re looking at half of the DNA,” said Samuel Newton, an assistant professor of law at the University of Idaho who has worked as both a prosecutor and public defender in Utah and Montana on death penalty cases. “So they could look at that one person’s half and compare it with the father’s known half. And then they know that this is the person’s son or father.”
That third method, used in genealogical testing, is called single nucleotide polymorphism, and it looks at thousands of binding sites in DNA compared to the 25 to 30 sites an STR analyzes.
“Genealogists have been using the SNPs, but the crime labs are just starting,” Hampikian said. “Police use either the FBI that does SNPs, or these private companies that do it for the genealogy.”
DNA labs report that it can take up to six weeks to thoroughly test DNA, but Hampikian said testing can take as little as a week.
Using genealogical DNA in court
During the Idaho Innocence Project’s investigation that led to the exoneration of Tapp, the organization also worked with the Idaho Falls Police Department to take DNA from the semen found on the victim using YSTR testing.
Idaho Falls police then acquired a subpoena for the database of Ancestry.com, which is a genealogy company that uses DNA and historical records to create family trees and connect people who may be related. Using the database, authorities obtained the last name of a potential suspect, which eventually led to the arrest of Brian Leigh Dripps.
It was the first time genealogy was used in a criminal case in Idaho, Hampikian said. But genealogical evidence has never been used in Idaho during a conviction in court.
“The FBI seems to be discouraging the mention of investigative forensic genealogy in probable cause affidavits,” Hampikian said. “ ... (The SNPs) have never been used directly in a criminal proceeding, even though that’s a great technology that gives you more information.”
Newton said DNA has been used in many major criminal cases regarding sexual assault and murder, but only by matching crime scene DNA to the suspect. And using DNA in court in any case can be difficult.
“Sometimes you’ll get mixed samples, and you have to kind of tease out who’s the predominant sample, or who they both are,” Newton said. “And there’s a lot of art to it that you really almost need an expert to mess with that stuff.”
Hampikian said he expects that a court challenge in 2023 will open the doors to SNP testing being more widely used. Another case in Idaho, which Hampikian said he could not identify, has only SNP evidence, and he hopes a judge will accept it.
Regarding Kohberger’s case, it remains unclear how much DNA evidence is involved.
“One of the challenges is that DNA can tell us nothing about how it got on something. Nothing about how long it’s been there,” Hampikian said. “So we don’t know if it’s from an original owner, from the current owner, the past owner, or someone deceased.
“When it’s on an object, DNA can’t tell us that. That’s for the triers of fact, the jury, to put together in their own head.”
