Idaho State Police have released images of the Ka-Bar knife sheath that Bryan Kohberger left behind at the University of Idaho crime scene, a key piece of evidence that helped authorities arrest him as part of a massive investigation into the quadruple homicide of four undergrad students in an off-campus home.

The photos were included in a public records release of more than 2,300 pages produced by state investigators.

Other evidence released includes handwritten notes from investigators, photos of nail clippings from the victims that were tested for DNA evidence and samples from Kohberger’s Hyundai Elantra that were tested at the crime lab.

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Forensic technicians tested the sheath for DNA evidence, ultimately recovering a sample on the snap.

The sample later turned into a tip developed by investigative genetic genealogists and ultimately led police to Kohberger’s parents’ home in Albrightsville, Pennsylvania, where he was arrested on Dec. 30, 2022.

He pleaded guilty in July and was sentenced to four consecutive prison terms of life without parole, plus another 10 years, for the murders of Madison Mogen, 21, Kaylee Goncalves, 21, Xana Kernodle, 20, and Ethan Chapin, 20.

IDAHO POLICE RELEASE INVESTIGATION PHOTOS OF KOHBERGER’S CAR AND CRIME SCENE WHERE FOUR STUDENTS DIED

According to the investigators’ notes, the victims left a sliding door open on the night of the attack for Goncalves’ dog, who was found unharmed in her bed. Goncalves and Mogen were both killed in Mogen’s bedroom.

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Many of the records had to do with crime lab work, including DNA testing, fingerprint analysis and other measures early in the investigation.

This is a developing story. Check back with Fox News Digital for updates.