Kelli Bordeaux, 23, was a combat medic at Fort Bragg, North Carolina. Her baffling disappearance shocked residents of Fayetteville, the quiet little southern town that Fort Bragg put on the map.

The mystery was all the more compelling in that Kelli was hardly your profile soldier. She was a former high school cheerleader and beauty queen whose good looks had always made her a magnet for male suitors. Kelli's gregarious, fun-loving personality also made her one of the most popular girls in her home town of St. Cloud, Florida.

The petite, 5'1" blonde was also as tough as nails. That, along with her passion for adventure and a dream of seeing the world, made the military a natural calling for her. And being a combat medic also satisfied Kelli's desire to help people.

Kelli had been stationed at Fort Bragg for only a couple of months since completing basic training and boot camp. Her husband of less than two years, Mike Bordeaux, had moved with her from St. Cloud, Florida, and the couple settled into an off-base apartment together.

David Marshburn, a private investigator who conducted his own investigation into Kelli's April 2012 disappearance, says the stress of adjusting to a new life in another state put their marriage under pressure, with Mike unable to find a job, and drinking heavily.

"She just had enough of him, from what I understand," said David Marshburn.

The couple would decide to take a trial break from each other, with Mike returning home to Florida and Kelli remaining alone in Fayetteville, where she knew no one other than her fellow soldiers at Fort Bragg.

But the private life of Private First Class Kelli Bordeaux was about to get complicated.

For about a year Kelli had been having an affair with a secret boyfriend named Justin Thompson, whom she'd met back in St. Cloud before joining the military.

Kelli's sister Olivia says Kelli liked Justin so much she had decided to divorce Mike Bordeaux, who had no idea his estranged wife already had a new man.

But it was during one of Justin's weekend visits to Fayetteville that Kelli met yet another suitor: Nicholas Holbert, who worked as a helper at a local bar called Froggy Bottoms, where Kelli and Justin had gone for drinks.

"Nick gave her his telephone number and tried to befriend her," said David Marshburn.

But P.I. Marshburn says Kelli thought of Nick only as a drinking buddy at Froggy Bottoms after boyfriend Justin had returned home to Florida.

"Nick offered to bring her back out there and she accepted," said Marshburn.

She returned to Froggy Bottoms with him the following Friday night. Kelli was never seen again after leaving later that night with Nick Holbert.

On the Friday night of April 13, 2012, that Pfc. Kelli Bordeaux disappeared, she was excited about going out to have some fun after another hard week at Fort Bragg in Fayetteville, N.C.

Kelli wouldn't drink and drive, so her new acquaintance Nicholas Holbert had given her a ride to Froggy Bottoms, where he worked as a general helper. Kelli had even told boyfriend Justin Thompson, who was living in Florida, that Nick was taking her to the bar.

And Justin, who'd met Nick with Kelli at the bar just a week earlier, wasn't happy about it.

"I said to be afraid of Nicholas. I told her he was creepy," Justin Thompson tells Crime Watch Daily.

"She was like, 'Oh, I'll be fine.' I even texted her that night before she left. I said 'You better bring your pepper-spray.'"

Private investigator David Marshburn, who conducted his own investigation of the Kelli Bordeaux case, says Nick considered their night at Froggy Bottoms a date -- but Kelli didn't.

"She was there to have fun. That's all it was. She was there as a friend. He was there trying to be a boyfriend," said Marshburn.

But Kelli just thought of him as a drinking buddy.

"They went to the bar and she basically didn't pay him any attention," said Marshburn. "She was singing, cutting up, flirting with other guys. Just being friendly."

Kelli would leave Froggy Bottoms with nick some time after midnight.

"She wasn't drunk," said Marshburn. "Her bar tab wasn't enough to make somebody dizzy."

Nick would later tell cops that he'd dropped Kelli off near her apartment.

And boyfriend Justin received a text from Kelli's cellphone later that night reading "Got home safe ... I'm going to bed ... Call me tomorrow."

"It was so weird because the text message before that was, 'Hey, call me. Call me. Call me,'" said Justin.

Justin Thompson did call her, constantly, all weekend, to no avail. So he alerted Kelli's family.

"And he's like something's up. Something's happened. Something's going on. And he knew immediately," said Kelli's sister Olivia.

Then, when Kelli doesn't report for duty at Fort Bragg on Monday morning, and there's no sign of her at her apartment, friends, family and Army brass really get worried. Kelli is reported missing to police and a massive search is mounted.

Among the search volunteers, Nick Holbert and Kelli's estranged hubby Michael Bordeaux, who, along with her boyfriend Justin, were the cops' main persons of interest. And because Nick was the last known person to see Kelli before she vanished, he was immediately under heavy suspicion.

But it seemed like everyone in Fayetteville had their own idea of who might have had something to do with Kelli's disappearance.

"The police department's number one person of interest, and I do know this for a fact, was the husband, not Nick," said Marshburn.

Mike Bordeaux had provided police with a verified alibi that he was at his home in St. Cloud, Florida, hundreds of miles from Fayetteville, North Carolina when his estranged wife disappeared.

Michael Bordeaux had his own suspect in mind.

"The first name I heard of was Justin," said Mike.

Pfc. Kelli Bordeaux had been keeping an intimate and perilous secret. The beautiful 23-year-old soldier had been having an extramarital affair for more than a year that her husband Michael didn't know about.

"The detective was the first person to tell me about it," said Mike.

Now, in exclusive interviews with Crime Watch Daily, Mike Bordeaux and Justin Thompson each talk for the first time about loving the same woman and living under a cloud of suspicion after Kelli's mysterious disappearance.

Police had no evidence to connect any of the three persons of interest to Kelli Bordeaux going missing.

Both estranged husband Mike and Kelli's boyfriend Justin had provided alibis that they were each hundreds of miles away in St. Cloud, Florida, when Kelli disappeared in Fayetteville, North Carolina.

And Nick Holbert, the last know person to see Kelli before she vanished, had told police he dropped her off near her apartment after an evening of drinking at a Fayetteville bar called Froggy Bottoms.

His story was supported by a text boyfriend Justin received from Kelli's cellphone later that night telling him she had arrived home safely.

Justin was unable to reach Kelli again -- and he suspected Nick had harmed her.

"I knew from the beginning when I talked to the detectives, I knew," said Justin. "I knew it was him."

And Justin Thompson wasn't the only one.

"I actually happen to see Nick Holbert on TV doing his interview on Kelli Bordeaux," said private investigator David Marshburn.

Holbert was pleading with the public for information on her whereabouts while he was out looking for her with hundreds of other searchers.

"And I told my wife, I said, 'Look, he's lying,'" said Marshburn. "I'm like a human lie-detector, just about. I can just tell when people are feeding me B.S. I feed people B.S. like you wouldn't believe, but it's my job."

David Marshburn is a private detective who's hunted down hundreds of fugitives wanted for jumping bail, and he was determined to go after Nick Holbert and solve the Kelli Bordeaux mystery.

"I told my wife, I said 'I want to see if I can find this girl,'" said Marshburn. "I can find somebody that's on the run, but finding somebody just sitting still, that's going to be another task."

Marshburn's suspicions about Nick grew when it was learned he was a homeless drifter living in his truck in a makeshift camp behind Froggy Bottoms, where he worked as a bar hand.

And then police discovered Nick Holbert was a convicted sex offender who had sexually assaulted and beaten a 5-year-old girl when he was 16.

Marshburn says Nick Holbert was a predator around females of any age.

Police still couldn't link Nick to Kelli's disappearance, but they did manage to put him behind bars for a year for failing to register as a sex offender in Fayetteville.

"So while he was in jail, the only thing I could do is go to areas where Nick had been, and I wound up working hundreds of hours searching woods, searching ponds, searching you know lakes, everything," said Marshburn.

When Marshburn fails to find any trace of Kelli, he devises a plan to befriend Nick when he gets out of jail and trick him into telling what he knows about Kelli's disappearance.

"I had to be his best friend. I had to be a good friend to him," said Marshburn. "I go within several days. And when he answered the door, I said 'Nick, I'm David Marshburn. I'm a P.I. I'd like to talk to you about Kelli. I don't believe you done it.'"

"I told him right out of the gate. 'But I believe you can help me to clear your name so we can find her,'" Marshburn said.

"I had it in three stages: You didn't have nothing to do with it, you might have had something to do with it, you did it. By the end of that you did it stage, I was accusing him of doing it and he won't deny it."

Marshburn would start by literally buying Nick's friendship and trust.

"The guy was down on his luck," said Marshburn. "He needed money, and if I gave him money, he would keep wanting to see me, whether I talked to him about Kelli or not. There were times when I would be at dinner with my family and he would call and said 'I don't have anything. I need some cigarettes. I need to eat.' And I would drop what I was doing, leave my family and go an hour away just to give him money."

But months would go by without a frustrated Marshburn getting any information out of Nick about Kelli's disappearance.

"I wanted to take him to a barn somewhere, start cutting his fingers off until he told me where the hell she was. That's how mad I was, how ticked off I was," said Marshburn. "I was so close, yet he wouldn't give it to me."

But Marshburn persisted, trying all kinds of ploys: One of them convincing Nick he'd worked out a deal with prosecutors, and presenting him with a fake plea bargain he drew up himself.

"I did a fake plea bargain with all this legal jargon that if you told me where Kelli was and apologized to the family he would get like probation and rehabilitation," said Marshburn.

"He's going to tell he committed murder, he killed Kelli. He's going to apologize for it, he's going to get mental health for it. He's going to stay in like an apartment complex where he'll have a computer to work on," said Marshburn. And Nick Holbert believed it.

"He took it, and looked at it, and stared at it, and read it over and over," said Marshburn. "Then all of a sudden he paused for a little bit, and then handed it back to me and said 'I'm not gonna sign it. They'll just take it back.'"

But the mere fact that Nick considered the deal was proof to Marshburn that he was responsible for Kelli's disappearance.

"At that point, two months into talking to him, that gave me the concrete evidence. I gotta get it out of him," said Marshburn.

For more than two years Kelli Bordeaux's family searched for answers, and they would finally get them when the private investigator managed to get one of the key players in the case to confess.

Wily private detective David Marshburn was just one more sneaky trick away from solving the Kelli Bordeaux mystery.

But when Nick Holbert backs out at the last minute, Marshburn comes up with a new ruse. This time, Marshburn convinces Nick he's about to be indicted for Kelli's murder.

"The reason I wanted to do an indictment is because I don't understand indictments. A lot of people don't unless you're in the legal realm. So an indictment will be easy to B.S. about and hard for him to understand," said Marshburn.

The crafty P.I. shows Nick a fake indictment he'd drawn up himself and gets him thinking he's under police surveillance.

"So I put a bondsman outside his house in a Crown Victoria, and he sees the Crown Vic and he said, 'I told you man, they're watching me,'" said Marshburn. "'They're coming after me. They got something.'"

Nick is suddenly ready to sign the earlier fake plea deal, accepting the phony offer of a hand-slap sentence in return for a confession. And he agrees to lead Marshburn to Kelli's body, buried in a wooded area near his makeshift camp behind Froggy Bottoms bar.

"As soon as we pull into Froggy Bottoms I can't even get the darn thing in park and he's jumping out and going straight back to where he killed her," said Marshburn.

Now Marshburn is finally about to learn the answers he's been seeking for the two years since Kelli went missing.

"And I walk over there to him and I put my hand up on his shoulder and I said 'Nick, are you ready to tell me?' He said 'Yeah.' I said 'Did you do something to Kelli?' He said yes."

And hours later at the crime scene, Nick also confessed to Fayetteville Police Detective Jeff Locklear.

And somewhere between what Nick tells Det. Locklear and what he'd earlier confessed to David Marshburn there lies the truth about what he did to Pfc. Kelli Bordeaux.

"His exact words were: 'While I was on top of her and she started screaming,'" said Marshburn.

Nick Holbert confesses the trouble began on that Friday night that he took Kelli to Foggy Bottoms, where he was working as a bar hand.

"So as the night went on she was ready to go home. She went to go pay her bar tab," said Marshburn. "Nick went ahead and went outside and was waiting in his car.

"And while she was paying her tab, the bartender told her 'Be careful of this guy, he's a sex offender,' and she had no idea."

"And when she came out she went down the sidewalk of Froggy Bottoms. She passes Nick's car and passes him and she's walking home. And he says, 'Hey, I thought I was taking you home.' She said '[----] you, you [----] child molester,' or something like that. So he ran up behind her and hit her, knocked her out," said Marshburn.

"He pulls her out, and lays her on the ground, and he pulls her clothes off. He goes ahead and starts having sex with her and his exact words were, 'While I was on top of her she started screaming,'" said Marshburn. "And he grabbed a rock and just beat her in the head with it. After a few seconds she was dead. He wrapped her head up with a trash bag."

Nick Holbert tells police he buried her nearby, then went back in and stayed at the bar.

Nick admitted that he'd sent the text message to Kelli's boyfriend Justin, then threw Kelli's phone into the nearby river after he'd already killed her.

Nick Holbert had led private investigator David Marshburn and his cadaver dog to a shallow grave where's Holbert had buried Kelli Bordeaux's body.

"So we dig down a little and find pieces of the jacket," said Marshburn. "So we're digging again and find the leg bone. We dig again, there's the whole jacket. We take the jacket and pull the whole jacket back and there she is, described with the bag on her head, the whole nine yards.

"I say a little prayer, and I said 'Baby girl, you are going home. You're going home baby girl,' and I'm starting to tear up now," said David Marshburn.

Holbert was arrested. He subsequently pleaded guilty to first-degree murder.

Holbert tried to apologize to Kelli's family at his sentencing hearing.

"Probably you and your family don't want to hear anything I have to say," Holbert said.

Kelli's mother Johnna Henson demanded he listen to her instead.

"I don't understand how you could take a beautiful young girl for pretty much no reason and beat the life out of her," Henson told Holbert.

Nicholas Holbert was sentenced to life in prison without the possibility of parole.

All thanks to David Marshburn, the persistent private detective who singlehandedly brought Holbert to justice and solved the Kelli Bordeaux mystery.

"He's doing it for my family and we don't even know. And I'm like, he's doing this just because he wants to make that difference. It's astronomical. It's more than my family could even show gratitude for," said Kelli's sister Olivia.

And Fayetteville Police admit they could not have closed the case without him.

Marshburn admits there were times he almost gave up. But he says he felt morally bound to keep going for the sake of Kelli and her family, and saw it as donating his time, skill and money to a worthy cause.

"That's the only way I give back. That's the only way I feel like it gets back to God's children, people that need it," said Marshburn.