Why Bryan Kohberger's Motive Is Not Important for Conviction—Ex-FBI Agent

The motive of the suspected killer of four University of Idaho students is not important for securing a conviction, according to a retired FBI agent.

Bryan Kohberger, 28, is charged with four counts of first-degree murder and one count of felony burglary in connection with the slayings of Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin.

A probable cause affidavit unsealed on Thursday revealed investigators used DNA evidence, surveillance footage and cell phone records to connect Kohberger to the crime. He was arrested at his parents' home in Pennsylvania on December 30 and returned to Idaho to face charges.

But one aspect of the case that the affidavit did not shed any light on was the motive for the killings.

Bobby Chacon, a retired FBI agent, said he believes investigators are gathering evidence that may shed light on Kohberger's motive.

"I think they've got an idea of the motive and they're looking for more evidence of that motive," he told NewsNation's Brian Entin on Sunday. But, it's not necessary to determine what the motive was to secure a murder conviction, Chacon said.

"As an investigator, motive was the least important thing I did...Because most murder statutes, you don't need to prove why somebody does it. My main thrust as an investigator was, who did this crime and how do I prove it? How do I help the prosecution get a conviction?" he said.

"The why of it was always the least important for me unless it led to other things in the investigation—unless it is to blunt a defense motion, a defense assertion that it was you know, self-defense or something like that."

The four students were found dead in an off-campus rental house in Moscow, Idaho on November 13. Goncalves, Mogen and Kernodle lived there with two roommates who were not harmed. Chapin was visiting Kernodle, his girlfriend.

Following the murders, weeks went by without an arrest and police released few details about the investigation, leaving the town on edge.

The affidavit revealed that Kohberger was on law enforcement's radar by late November and that a warrant for his arrest was requested after DNA taken from trash outside his parents' home was matched with DNA on a knife sheath recovered at the crime scene.

A Pennsylvania native, Kohberger had arrived in Pullman, Washington—just across the state border from Moscow—sometime last summer to begin his doctoral studies in criminology at Washington State University.

According to the affidavit, cell phone records show his phone was near the area where the murders occurred at least 12 times prior to November 13.

Investigators will continue to look into what the motive was because prosecutors "always like to tell the jury the story of why this happened," Chacon said. "But the why certainly is not needed for a conviction. It's not required by the statute."

Determining a motive is "always the most nebulous part of a case like this," Chacon added. "Because quite frankly, there is no rational reason to do this and when we find out the why it will be very unsatisfying."

Prosecutors, attorneys and investigators can no talk about the case after Judge Megan Marshall issued a gag order last week prohibiting any of the parties from talking about anything "reasonably likely to interfere with a fair trial."

But Jason LaBar, the public defender who represented Kohberger in Pennsylvania, previously said Kohberger is "eager to be exonerated."