Kohberger is accused of fatally stabbing 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.
In the state's filing released Tuesday afternoon, prosecutors summarize a defense filing that appears to be sealed.
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"Instead of challenging the conclusion that the DNA on the knife sheath belonged to Defendant, the defense's expert disclosures reveal that the defense plans to argue the DNA on the knife sheath does not prove Defendant was ever at the crime scene and the knife sheath itself could have been planted by the real perpetrator."
The prosecutors' filing quotes a defense expert disclosure that prosecutors say reveals Kohberger's lawyers intend to call an expert in forensic biology and DNA who will testify that "[t]here is good support that Mr. Kohberger's DNA was found on Item 1.1, a swab from the knife sheath."
No further information from the defense expert disclosure is provided in the prosecution's filing dated March 10 and any response from Kohberger's lawyers has not been made public.
The DNA recovered on the button of the knife sheath, which ultimately led investigators to Kohberger, is a key piece of evidence in the case and has been the subject of multiple motions ahead of trial.
The Idaho state lab first 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.
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 have said.
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.
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A cheek swab from Kohberger confirmed he was a "statistical match" to the knife sheath sample, court documents show.
Kohberger's defense team has repeatedly questioned the use, legality and accuracy of the DNA testing done in each step of the process.
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The new glimpse into Kohberger's potential defense strategy comes in a filing from Idaho state prosecutors saying they are willing to agree with the defense position to exclude trial evidence related to IGG.
Prosecutors say they only plan to refer to the IGG material as a generic tip without revealing the source or the substance of the tip, the filing says. They'll ask an investigator on the stand to testify that law enforcement received a tip and that based on the information and other evidence, authorities eventually identified Kohberger as a suspect.
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