- Defense alleges knife sheath DNA could have been planted by 'real perpetrator'
- Prosecutors used genetic genealogy to link Kohberger to crime scene evidence
- Trial expected to last 3+ months with 40+ witnesses
- IGG evidence excluded despite initial investigative use
In a dramatic turn for one of Idaho's most high-profile murder cases, prosecutors disclosed this week that Bryan Kohberger's legal team plans to challenge forensic evidence through an unprecedented defense strategy. The 28-year-old criminology student stands accused of fatally stabbing four University of Idaho undergraduates in a 2022 attack that shocked the rural college town of Moscow.
At the heart of the controversy lies a leather knife sheath discovered near victim Madison Mogen's body. While prosecutors maintain that Kohberger's DNA conclusively matches genetic material found on the sheath snap, defense attorneys argue this evidence proves nothing more than secondary transfer. Legal analysts suggest this approach could mirror the 'third-party culpability' strategies used in high-stakes California cases like the Kristin Smart murder trial.
Forensic experts interviewed by Northwest Legal Review note that touch DNA—the type found on the sheath—can remain detectable for weeks and transfer through multiple surfaces. This raises questions about whether the genetic material could have been inadvertently moved via first responders or investigators, a concern previously documented in 17% of cold cases reviewed by the Idaho State Crime Lab.
Prosecutor Bill Thompson's motion reveals the state will avoid mentioning investigative genetic genealogy (IGG) during trial, despite using the technique to initially identify Kohberger. This decision follows defense challenges to IGG's scientific validity, though Judge Hippler ultimately permitted limited use of the DNA results. The prosecution now faces the delicate task of explaining Kohberger's arrest without referencing the controversial DNA-sleuthing method that combined commercial databases with family tree research.
With jury selection scheduled to begin August 11, legal observers predict the defense will emphasize alternative suspect theories and crime scene contamination risks. The defense team's sealed expert witness list reportedly includes specialists in digital forensics and blood pattern analysis, suggesting challenges to both the physical evidence timeline and Kohberger's alleged cellphone pings near the crime scene.