Did he use my knife to slaughter his victims? 

That's the chilling question Mark Baylis has asked himself ever since Bryan Kohberger was arrested for the November 13, 2022, murders of four University of Idaho students.

More than two years later, Kohberger has now finally confessed to breaking into the students' home in Moscow, Idaho, and stabbing Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin to death.

Baylis, a 64-year-old Special Forces veteran, knew Kohberger many years before he became a killer.

His son Jack and nephew Brandon grew up with Kohberger, now 30, in the Pocono Mountains of Pennsylvania and would often hang out together at Baylis' home deep in the remote woods of Saylorsburg.

'He was my nephew's friend and when we had family gatherings over here, if he was at my nephew's house, he would come over,' Baylis told the Daily Mail.

Then, Baylis said, there was a series of break-ins at his home in 2013.

'Somebody was coming into my house when nobody was home and taking weird things,' he recalled, including knives, his military clothing, prescription drugs, jewelry and a stash of coins from his collection.

Bryan Kohberger (pictured) is suspected of committing home break-ins in Pennsylvania in the years before the murders

A Ka-Bar knife and sheath (stock image) like the type believed to have been used in the murders

It was around that time that a teenage Kohberger began using drugs, which escalated into a years-long heroin addiction.

Baylis said he reported the break-ins to police at the time, but the burglar was never caught.

It was only years later - when Kohberger was arrested for murder - that Baylis connected the dots and realized the culprit was likely hiding in plain sight all along.

'I'm reasonably sure that he did it because, as soon as he moved away, the incidents stopped,' Baylis said.

'That raised a red flag for me - now I know who it was.'

But, even more concerning than the belief that a budding killer was breaking into his home was the terrifying realization that his possessions could have been used to commit a far worse crime 2,500 miles away.

Baylis told the Daily Mail he has 'a nagging suspicion' that he used to own Kohberger's exact murder weapon.

'I wouldn't want it to be something I used to own.'

Baylis said several knives had been taken from his home during the break-ins - including Ka-Bar knives like the one Kohberger is believed to have used to kill the students.

Ethan Chapin, Xana Kernodle (both left), Madison Mogen and Kaylee Goncalves (both right)

Bryan Kohberger broke into 1122 King Road in Moscow, Idaho, on November 13 2022 and murdered the four victims

Camillus knives - the company which previously manufactured Ka-Bar knives - were also taken.

Baylis said he gets a 'sick feeling in my stomach' thinking about the possibility the incidents could be connected.

Investigations following the murders revealed Kohberger stabbed each of the four victims multiple times with a large knife.

During the frenzy, he left a leather Ka-Bar knife sheath - featuring a USCS military seal - behind at the scene. It was found next to Mogen's body inside her bedroom on the third floor of the home.

Amazon records show Kohberger bought a Ka-Bar knife and sheath using a gift card in March 2022 - eight months before the attack.

The items were delivered to his parents' home in Albrightsville, Pennsylvania, where he was living at the time.

Following the killings, prosecutors said he searched to buy a replacement knife and sheath.

But the murder weapon itself has never been found, so the exact knife used remains unclear. 

In the hours after the murders - both as soon as he left the scene and in the afternoon of November 13, 2022 - records show Kohberger drove through rural areas of Idaho and Washington, including close to the Clearwater River and the Snake River.

It is possible he disposed of evidence along the route, though this remains unproven.

Following Kohberger's December 2022 arrest, Baylis said he contacted local police asking them to reopen an investigation into the burglaries but was told the case was too old.

Pennsylvania State Police have not returned the Daily Mail's request for information and comment.

Baylis wonders if the truth could lie in the cameras that have lined his property for years.

'I have a couple game cameras still in the trees around my house that have been up there for a long time,' Baylis said.

'I haven't checked the cards. It would be interesting if I had pictures of him there.'

But, he said part of him doesn't want to know if the mass killer's murder weapon was once his.

'I would love to see the picture of whatever the murder weapon was, but maybe I don't want to,' he said.

Baylis isn't the only person who believes that night in November 2022 wasn't Kohberger's first crime - or specifically the first time he committed a burglary.

In the new book, The Idaho Four: An American Tragedy, James Patterson and Vicky Ward reveal that another woman, Connie Saba, has also long suspected he broke into her home.

Connie's son Jeremy Saba and Kohberger were friends growing up, and both grappled with heroin addiction.

In August 2016, Jeremy was jailed for driving under the influence and possession of drugs, the authors write.

After hearing the news, Kohberger called Connie who told him what time she and Jeremy's father, Jiries Saba, would be visiting him at the jail the following day.

Bryan Kohberger seen in his yearbook photos in his sophomore year (left) and senior year (right) at Pleasant Valley High School

Connie said Kohberger promised her he would visit Jeremy at the jail straight after them.

But he failed to show up.

When Connie and Jiries arrived home, they found their house had been burglarized -  Patterson and Ward said they were only gone for a short window of time.

'The Sabas' absence from their home gave him the perfect window to get what he needed. He used to live next door, so he knew the house, knew where Connie kept her jewelry and where she left her iPad, things he could sell to get his next fix,' the authors wrote.

'And he knew exactly how to break in: through the garage.'

Connie said she thought about calling the police and Kohberger's parents but decided to do neither. 

'She intuits that the Kohberger family is in enough pain right now without Connie Saba adding to their problems,' according to Patterson and Ward.

Connie claimed that, in 2018, Kohberger - who was clean from drugs after multiple rehab stints - turned up unannounced at her home to apologize for stealing.

'I knew it was you,' Connie recalled telling him.

Her son Jeremy died in 2021 from a fentanyl overdose.

Kohberger, meanwhile, turned his attention to studying criminology, first at DeSales University in Pennsylvania and then at Washington State University in Pullman.

He moved to Pullman in June 2022, and five months later, he broke into another home - this time with a plot to kill.

It was around 4am on November 13, 2022, when Kohberger entered 1122 King Road through a sliding back door on the second floor.

He made his way up to the third story and went straight to 21-year-old Mogen's room where he found her and her best friend Goncalves, 21, sleeping in the same bed. He stabbed both of them to death.

On his way back downstairs, he encountered Kernodle, 20, on the second floor, who had just received a DoorDash order.

He attacked her with the knife, killing her, and then also murdered her boyfriend, Chapin, 20, who was sleeping in her bed.

Kohberger then left via the same door through which he entered, passing roommate Dylan Mortensen along the way, who woke up from the noise and peeked out her bedroom door.

Mortensen and roommate Bethany Funke - whose bedroom was on the first floor - were the only survivors.

Terrified after seeing a masked man inside the home, Mortensen and Funke desperately tried to call and text their friends but got no response.

Ultimately, Mortensen ran down to Funke's room on the first floor where they both stayed until daylight.

Bryan Kohberger snapped this selfie hours after murdering the four students

Around eight hours later, a 911 call was placed alerting officers to the home. 

On July 2 - after two years of protesting his innocence - Kohberger admitted his guilt. 

As part of a plea deal - which proved controversial among the victims' families - he pleaded guilty to avoid the death penalty.

Under the terms of the plea deal, he will be sentenced to life without the possibility of parole and will also never have a chance to appeal his conviction or sentence.

His motive for the murders - and why he targeted his victims - remains a mystery.  

Kohberger will return to Ada County Court in Boise to be sentenced on July 23.