CNN
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In its case against Bryan Kohberger, the man accused of killing four University of Idaho students in November 2022, the prosecution’s most important piece of evidence may be a DNA sample taken from a knife sheath left at the crime scene.
But several other pieces of DNA evidence, including a sample from fingernail clippings taken from a victim and bloodstains from unknown male sources, could also play key roles in the upcoming trial.
On the knife sheath DNA, authorities used investigative genetic genealogy – or IGG – a field of forensic science combining DNA analysis with genealogical research, to connect that sample to Kohberger’s family, prosecutors said in a January hearing. Subsequent DNA testing found Kohberger was a “statistical match” to the sample, leading to his arrest.
But challenging the legality, accuracy and use of DNA analysis also appears to be a main focus for Kohberger’s defense team – as suggested by witness testimony in the recently unsealed transcript of a closed court hearing. The defense has also hired Bicka Barlow, an attorney specializing in forensic DNA evidence.
During the closed hearing in January, testimony from witnesses raised questions about how investigators used the DNA sample from the knife sheath to identify Kohberger as the only suspect in the killings.
“The DNA could make or break the case, and it’s all about what the jury finds to be credible,” Misty Marris, an attorney who has closely followed the case, told CNN.
Kohberger is accused of murder in the brutal stabbings of Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin at an off-campus home in Moscow in November 2022. Not guilty pleas have been entered on his behalf and his trial is set to begin in August. He faces the death penalty if convicted.
Here’s a closer look at the DNA evidence in the case:
The Idaho state lab located a single source of male DNA left on the button snap of the knife sheath found on the bed next to Mogen’s body at the crime scene. The DNA of Bryan Kohberger is a “statistical match” to that DNA, court documents filed by prosecutors state.
Samples from the sheath were tested for “touch DNA,” which can be skin cells shed on items while being handled, said Rylene Nowlin, an Idaho State Police forensic laboratory manager, during the January hearing. That DNA was key evidence for investigators, Moscow Police Cpl. Brett Payne, the lead detective in the case, said at the same hearing.
Idaho State Police delivered the knife sheath sample to Houston-based Othram laboratory for further testing, Nowlin said. The FBI took over the testing on December 10, and nine days later, the agency gave Idaho investigators Kohberger’s name for the first time.
“The DNA from the knife sheath was obviously the one thing we had that we thought was a very strong piece of evidence in this case, so it was that particular piece that we pursued as a potential avenue of identifying a suspect,” Payne said during the January hearing.
Investigators then went to Kohberger’s family home in Pennsylvania and pulled items from the family’s trash to test against the knife sheath sample. A DNA profile obtained from the trash was identified as “as not being excluded as the biological father of Suspect knife Profile,” according to court documents.
“At least 99.9998% of the male population would be expected to be excluded from the possibility of being the suspect’s biological father,” court documents state.
Finally, investigators took a cheek swab from Kohberger, conducted a short tandem repeat – or STR – test, and found he was a “statistical match” with the knife sheath DNA, according to prosecutors. An STR analysis is a common type of DNA profiling in criminal cases, according to the National Institute of Justice.
“In a field of haystacks, IGG gives you the haystack to look in,” Steve Kramer, a former attorney for the FBI who was among a team of investigators who used genetic genealogy to solve the Golden State Killer case, told CNN. “STR finds the needle in the haystack.”
A three-person mixture of unknown DNA was found under 21-year-old University of Idaho student Madison Mogen’s fingernails after she and three other students were killed at their off-campus home, a recent filing in the case revealed.
The DNA was taken from a swab of fingernail clippings from Mogen’s left hand, according to the motion, filed by Kohberger’s defense team. Fingernail clippings are routinely taken by medical examiners during autopsies and forensic testing is performed on them.
The new filing showed preliminary testing was done on the fingernail clippings and a “likelihood ratio” was calculated which, according to the defense, proved to be inconclusive. The testing did provide a “likelihood ratio for Mr. Kohberger” from the analysis – but any conclusion is redacted in the filing.
The testing involved a comparison of hypotheses, “not a statement of identity or probability of identity,” according to the defense motion.
Two hypotheses were looked at: One is that the DNA belongs to Madison Mogen, her best friend Kaylee Goncalves and one unknown unrelated person. The other is that the DNA belongs to Mogen and two unrelated individuals, the defense filing states.
Mogen, a senior marketing major, and Goncalves, a senior general studies major, were found dead on the same bed at the Kings Road home on November 13, 2022.
The defense asked that the DNA evidence be kept from the jury in Kohberger’s upcoming death penalty trial because jurors could believe the DNA is Kohberger’s, and according to the defense, it is not.
“Allowing such testimony would violate Mr. Kohberger’s Federal and State Constitutional rights to due process, a fair trial, effective assistance of counsel, and confrontation of witnesses,” according to Barlow.
“When you see it under the fingernails, the argument is going to be … that there’s a scratch, that somebody fought back,” said Marris.
“From the prosecution perspective, the argument is, well, it’s not necessarily, because there’s lots of different ways DNA can end up somewhere.”
At the January hearing, Kohberger’s defense also closely questioned lead detective Payne about blood found on a handrail between the first and second floors of the home, connected to “Unknown Male B.” Payne said police did not pursue that person because, “We had already received Mr. Kohberger’s name.”
The defense also raised the issue of blood on gloves found outside the house, connected to “Unknown Male D,” which Payne acknowledged.
It was not clear from the transcript of the hearing if law enforcement pursued the identity of “Unknown Male B” or “Unknown Male D” at a later time. “So, if memory serves, the discussion was we’ll hold off, we’ll stay with the one from the knife sheath; if we need to, we can address the ‘Unknown Male B’ at a later time,” Payne testified.
The defense will likely argue that there’s reasonable doubt that Kohberger committed the murders, Marris explained.
“Their argument is going to be that once that investigative genetic genealogy match was made and Kohberger was identified that law enforcement essentially put on blinders,” she said. “They didn’t care about anything else, so much so that they didn’t even care that there is additional DNA evidence.”
To prove reasonable doubt, the defense will likely argue that there was a significant failure in the investigation to pursue any and all possible paths to find the culprit in a heinous crime, Marris said.
“You have this entirely other set of potential DNA that could have led investigators, had they pursued it, to somebody else, and that’s going to be a huge component of the argument.”
