The Idaho student murders suspect may not have forgotten the Ka-Bar knife sheath found in a bed with two of the four victims – it may have been planted there in an effort to mislead investigators, according to a criminal profiler who has been following the case.

"If you took a pistol out of your holster, wouldn't you put it back in?" asked John Kelly, a psychotherapist with experience interviewing serial killers, in an interview with Fox News Digital. "I don't know anybody who wouldn't, and if I went fishing and had to take my knife out, I would put it back in the sheath."

It's a reflexive action, he said, adding that a vegan like murder suspect Bryan Kohberger likely put the knife away somewhere in order to keep the blood from contaminating his clothes or vehicle.

"You're such a clean vegan who's obsessive-compulsive about what you eat and everything else, just the hygiene of carrying a bloody knife around, wearing it somewhere on your person as you get out of the house," he said. 

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The answer may hinge on what a surviving housemate, the only eyewitness, saw that night.

A police affidavit states that she heard noises, including whimpering and crying, and then saw a masked man with "bushy eyebrows" leaving through a sliding door. It makes no mention of seeing an intruder carrying a weapon.

"The girl didn't say anything about seeing a knife," Kelly said. "Did he put it in his clothes somewhere and have blood all over?"

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Kelly believes that the sheath may have been left intentionally – after being wiped clean of fingerprints but not thoroughly enough to remove the touch DNA evidence that police found on the snap.

The attacker could have put the knife in a different sheath or some other sealed container and left the "USMC"-stamped sheath behind in an effort to cast suspicion on someone with ties to the military, Kelly said. 

"This is staging 101," he continued. "They're gonna look at this, and they're gonna think it's a military guy that did this. Some guy with some kind of training who lives up the road."

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However, police recovered DNA on the snap that they later said matched a familial sample taken from the trash at Kohberger's parents' house 2,500 miles away in Pennsylvania.

"He may have thought this was the perfect ruse, again he's no genius, his ruse and staging set him up to get caught," Kelly said. 

If he had simply forgotten the knife, police may have found more DNA on the sheath along with fingerprints, Kelly said. As of a gag order on Jan. 3, police had still not recovered the murder weapon.

"That could have precipitated the question, ‘Who else did you arrest?’" Kelly continued, referencing a rumored statement that Kohberger made to police when they took him into custody on Dec. 30. "I think he had to believe that that was gonna lead them to somebody, some direction, with the sheath there."

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Kelly's hypothesis is "not unreasonable," said Paul Mauro, a retired NYPD inspector who is also an attorney.

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"[The] other side of that would be that he was mentally in an altered state," he told Fox News Digital.

Kohberger, a criminal justice Ph.D. student at Washington State University, is accused of entering a six-bedroom rental home near the University of Idaho campus just 7 miles away around 4 a.m. on Nov. 13, 2022.

Inside, police say he ambushed four students, some of whom may have been sleeping, with a large knife.

The following day, police found 21-year-old best friends Kaylee Goncalves and Madison Mogen dead in a bed on the third floor. On the second level, they found housemate Xana Kernodle, 20, and her visiting boyfriend, Ethan Chapin, also 20. All four had been stabbed multiple times.

Kohberger faces four counts of first-degree murder and a felony burglary charge. 

He could face the death penalty if convicted. He's being held without bail and due back in court on June 26.

Judge Megan Marshall issued the initial gag order Jan. 3, shortly after Kohberger's arrest, restricting comment from prosecutors, the defense, law enforcement and other officials.