The forensic criminologist hired by the defense in Bryan Kohberger’s murder case argued that one person alone could not have killed the four University of Idaho college students

Bryan Kohberger appears for a hearing at the Ada County Courthouse on July 2, 2025, in Boise, Idaho.Credit : Kyle Green-Pool/Getty

“At least two suspects were involved in this attack.”

That is what Dr. Brent Tarvey said after reading the autopsy reports of Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin.

The forensic criminologist was hired by Bryan Kohberger’s defense team to help defend the then-murder-suspect at trial and outlined why he believed it would have required two people to kill the four University of Idaho students at 1122 King Road on Nov. 13, 2022.

That outline is still under seal, however, but sections of Tarvey’s findings are included in a separate court filing that was recently unsealed and obtained by PEOPLE.

“It is not reasonable to think that Ethan would have remained in his bed after waking up or being awake while Xana was being attacked in front of him. This evidence and context begin to suggest the existence of a second attacker,” Tarvey wrote in his report, according to the unsealed filing.

He later wrote that because “Ethan and Xana appear to have been attacked at the same time,” it is “inconsistent with the State’s theory that these crimes were committed solely by one individual.”

This claim is based on the fact that an autopsy report determined Chapin never stood up or left the bed where he was found dead on the night of the murder.

Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin.Idaho Statesman/Tribune News Service via Getty

Prosecutors responded to this argument in the unsealed filing, writing: “One assailant could contain two people in close proximity to each other, especially if the assailant is armed.”

Tarvey next turned his attention to one of the other victim’s autopsy reports, which found “that multiple types of lethal force were used against Kaylee.”

In response to this argument, prosecutors wrote: “A single perpetrator … can use multiple types of lethal force.”

The final argument Tarvey made in support of his theory had to do with time — specifically the approximately 15 minutes the suspect spent at the crime scene on the night of the murders.

“The precautionary acts in this case include the execution of living witnesses; the clean-up of bloody hands, feet / foot-ware and clothing before leaving; and the disposal of said clothing along with the weapons used,” Tarvey wrote in his outline, per the unsealed filing.

He went on to claim that there was “direct evidence of this clean-up,” pointing to the fact that there were traces of blood found on the walls and common area of the home that had been diluted by an unknown substance.

There was also “indirect evidence,” he alleged, such as “the absence of bloody footwear patterns at the scene in general.”

Tarvey argued that one person could not have cleaned up these bloody footprints and wiped down the walls and still be out of the house in 15 minutes, which strongly suggested in his mind that this was a two-person job.

“Washing or wiping hands takes little time especially if preparations for cleaning are made beforehand,” prosecutors wrote in their response. “Removal of protective clothing and shoe coverings takes seconds.”

Tarvey used a similar argument to defend Kohberger, pointing out that the person who murdered the four students transferred the blood throughout the house. But, when police impounded Kohberger’s car after his arrest on Dec. 30, 2022, there was not a single trace of blood or DNA belonging to any of the victims found inside.

“Despite an extensive and exhaustive forensic examination of the Defendant’s vehicle for bloody clothing, blood transfer, and other evidence related to these crimes — down to the metal — none was found,” Tarvey wrote.

He continued by arguing that this “excluded the Defendant’s vehicle as being related to the commission of these crimes,” adding that the “failure to be absolutely clear and forthcoming about this evident fact would be evidence of bias.”

In response, the State said there “can be a myriad of reasons blood was not transferred to or detected in the Defendant’s vehicle.”

Kohberger’s attorney Anne Taylor with his mother MaryAnn and sister Melissa (l to r).AP Photo/Drew Nash

Another expert hired by Kohberger’s team similarly tried to argue he could not have been responsible for the crime, according to a prosecution filing responding to that expert’s argument and obtained by PEOPLE.

“Through his other expert, Rachel Orr, [Kohberger] has also submitted evidence that he suffers from Developmental Coordination Disorder, which has resulted in deficits in fine motor dexterity and visual motor function,” prosecutors wrote in that filing.

“His attorneys have argued in other motions that these deficits render it ‘not possible’ for Mr. Kohberger to have acted with the speed and coordination required to commit the crimes in the time frame alleged by the State.”

Kohberger ultimately decided to enter guilty pleas to all four counts of murder just before his trial was set to start. He agreed to a deal with prosecutors that spared him the possibility of being sentenced to death in exchange for the pleas.

Kohberger is now serving four life sentences and will never be eligible for parole.