Bryan Kohberger DNA a "statistical match" from Idaho murders knife sheath: court documents
(CNN) -- The DNA of Bryan Kohberger, the suspect in the stabbing deaths of four University of Idaho students at an off-campus home in Moscow last fall, is a "statistical match" to DNA collected from the sheath of a knife found at the scene, according to court documents filed by prosecutors.
An "STR" DNA comparison was performed on DNA collected from Kohberger and DNA taken from the knife sheath, prosecutors said in the June 16 filing. The samples showed a "statistical match," the court documents state.
An "STR" analysis – or short tandem repeat analysis – is a common type of DNA profiling in criminal cases and other types of forensic cases, according to the National Institute of Justice.
"The STR profile is at least 5.37 octillion times more likely to be seen if (the) Defendant is the source than if an unrelated individual randomly selected from the general population is the source," prosecutors said in the filing. An octillion is a number equal to a 1 followed by 27 zeros.
The FBI originally loaded the DNA profile from the knife sheath onto publicly available genealogy sites, the documents state.
"The FBI went to work building family trees of the genetic relatives to the suspect DNA left at the crime scene in an attempt to identify the contributor of the unknown DNA," and then sent a tip to investigate Kohberger, according to prosecutors.
That tip "pointed law enforcement toward (the) Defendant, but it did not provide law enforcement with substantive evidence of guilt," according to the prosecutors' filing – which is why they followed up using an STR analysis.
A DNA sample from trash recovered from the Kohberger family residence by Pennsylvania law enforcement and sent to the Idaho State Lab for testing was also used to help investigators home in on Kohberger as a suspect in the killings, court documents released earlier this year state.
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Those documents also say a DNA profile obtained from trash at the home and the DNA profile obtained from the sheath, "identified a male as not being excluded as the biological father of Suspect knife Profile," the documents state.
"At least 99.9998% of the male population would be expected to be excluded from the possibility of being the suspect's biological father."
Killings shocked community
Kohberger faces four counts of first-degree murder and one count of burglary in the November 13 killings of Kaylee Goncalves, 21; Madison Mogen, 21; Xana Kernodle, 20; and Ethan Chapin, 20, at a home just outside the university's main campus in Moscow. A not-guilty plea was entered on his behalf by an Idaho judge at a hearing last month.
The killings and subsequent lengthy investigation rattled Moscow, a city of 25,000 people that hadn't recorded a murder since 2015.
After weeks of little information and heightened anxiety in the community, Kohberger was arrested at his parents' home in Pennsylvania in late December and identified by authorities as the alleged killer. He has been in police custody since and is being held without bail.
RELATED: Knives, gun found at Idaho murders suspect Bryan Kohberger's Pa. home: court documents
At last month's hearing, Judge John Judge read aloud Kohberger's rights and each of the charges outlined in the indictment. When asked if he understood the charges, Kohberger replied to each, "Yes."
When asked for his plea to the counts, Kohberger remained silent. His attorney rose and said, "Your honor, we are standing silent," and the judge then entered not guilty pleas for him.
A gag order implemented in the case prohibits all attorneys – prosecutors, defense lawyers, and those representing victims and witnesses – from saying anything publicly beyond what is already in the public record.
