A knife sheath, fingernails and bloodstains: A closer look at the key DNA evidence in the Idaho killings case

In the 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 is a DNA sample taken from a knife sheath left at the crime scene.

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.