Idaho murder investigators can identify the knife without it ever being found: Forensic expert

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Forensics expert explains how metal fragments can be used to identify the Idaho murder weapon

A forensics expert explained to Dr. Phil how chips from the knife can be recovered during autopsy and analyzed by scientists to find critical clues, even if the murder weapon is never recovered. 

The knife used in the Idaho student murders may have left behind evidence that investigators could use to tie it back to the killer, even if the blade is never found, one forensic expert said.

In the early hours of Nov. 13, University of Idaho students Kaylee Goncalves, Madison Mogen, Xana Kernodle, and her boyfriend, Ethan Chapin, were stabbed to death, allegedly by Washington State University graduate student Bryan Kohberger. An empty tan leather knife sheath was found next to the bodies of two of the slain students and police say the murder weapon is a fixed-blade knife.

While the knife itself is still missing, forensics expert Joseph Scott Morgan described on "Dr. Phil" Thursday how the weapon could still be identified and linked to the killer.

"It’s not necessary that we have the knife at this point because the knife actually could leave behind more evidence," Morgan explained.

Experts appearing on Dr. Phil theorized about the weapon used in the Idaho murders.

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He said the full body x-ray done during autopsy may reveal a metal chip from the knife that can then be analyzed. 

"So, this knife, allegedly, has been used repeatedly — four times, ok? Let’s just think about that. The structural integrity of this thing begins to wear down," Morgan said. "It’ll chip. Sometimes points break off. I’ve seen this any number of times at autopsy. If that is the case, they may very well have recovered a metal fragment from the blade of that knife within the body."

He then explained how metallurgical analysis can be used to trace the knife back to its specific manufacturer, which could then help investigators figure out where the knife was sold and who purchased it.

Police suspect a Ka-Bar knife may have been used in slayings of four University Idaho students, inset. Caution tape surrounds the house near campus where the students were slaughtered. (Credit: Ka-Bar / Derek Shook for Fox News Digital)

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"Just because the sheath was found there, doesn’t mean that that’s the knife that was carried. So you look for a specific forensic tie-back relative to the chemical structure of the blade as well. That might be a potential here in this case," Morgan noted. 

Trial attorney Mercedes Colwin speculated the knife’s sheath may have been left at the crime scene on purpose.

Dr. Phil speaks with his guests on an episode about the Idaho murder suspect. (CBS screenshot)

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"It could be, I mean, it’s almost as if – and we’ve seen this with other killers, it’s their calling card, ‘I got this,’" she said. "Especially if you think you’re smarter than everybody else, and he certainly – he had gloves, at least that’s what’s presumed, that he had gloves. He tried to cover himself, did something to dispose of the clothing, if he in fact is the killer, then, of course, this is something that could have just been a calling card and left it there."