A handsome military veteran seemingly vanishes into thin air after spending the night with his friend. Where on Earth is Chase Massner?

That question leaves his mother and wife begging for answers. The mystery haunts cops for years and captures the nation's attention, until a deeply buried secret uncovers a devastating surprise.

Chase Massner was a strapping 6' 2" Iraq War veteran, a devoted husband and father of two beautiful girls.

After a year overseas, 26-year-old Chase returned home to the small Southern town of Kennesaw, Georgia, about 20 miles north of Atlanta. But tormented by his own demons, his wife Amanda says Chase struggled with bipolar disorder.

"We've had some hard times with his mental stability," Amanda said.

The last time Amanda saw Chase alive was unfortunately when they were arguing in the car in March 2014.

"He wants to walk away, but obviously I'm not going to let him just walk away," Amanda Massner said.

To cool off, she dropped Chase off in the parking lot of the convenience store where he worked the night shift.

"He's threatening to jump out of the car and punching the dash," said Amanda.

Amanda hoped to see him after work, but Chase spent the night at his friend Brad Clement's house, reports Crime Watch Daily affiliate CBS46 WGCL-TV.

It wasn't especially strange -- until 24 full hours pass and nobody hears from Chase. His mom, Stephanie Cadena, calls his cellphone, hoping he'll pick up. But a mother's love is not enough to get a return call. And as the hours tick by, worry turns to sheer panic.

Stephanie calls the Cobb County Police Department, but cops say that since Chase has left on his own accord there's no reason to suspect foul play. They agree to a brief walk through Brad's home. Nothing seems suspicious. So with growing frustration and little help from the police, Chase's mother and his wife deploy troops of their own, launching a feverish search with more than 100 volunteers. They blanket the town with flyers, hold vigils and set up Facebook group "Team Chase" with updates on their search.

Six excruciating months pass, but no trace of Chase Massner is found. But at least the right questions will soon be asked. Now realizing Chase didn't disappear willingly, cops officially open an investigation and turn their sights on Chase's buddy Brad, the last known person to see him alive.

Brad Clement declines to take a polygraph test, saying his emotions are all over the place, but he agrees to speak with police. It would only be another frustrating dead end. The interviews yield no clues and cops don't name Brad a suspect.

Despite claiming his innocence, Brad Clement says he received a barrage of nasty comments on social media. To lift the veil of suspicion, he agreed to speak on camera.

"The whole reason I got into this was to help the guy," Brad tells a local reporter.

Brad reasoned that if he was guilty in any way, why would he stay in town?

"I've been here in Atlanta. Like, I haven't tried to disappear," Brad says.

But there was still the burning question that Chase Massner's family needed answered.

"Did you have anything to do with the disappearance of Chase Massner?" Brad is asked.

"No, I did not," Brad replies. "I had nothing to do with him just completely disappearing off the face of this Earth."

Brad Clement says that the night Chase slept over, they stayed up all night talking about his marital problems.

"I was in no way part of anything, other than just trying to help him work something out with his wife," said Brad.

The next morning, Brad says, he ran errands while Chase slept. When he returned, his friend was gone. That's when he also called Chase's cellphone.

Brad Clement: "Hey man, what's up? Where did you go, dude? I just got back from having to run down to town. The roofing guy said you left like two hours ago or something, I think. They just left out of here, but call me man. Let me know what's going on. See ya."

Here's what Brad said about that message, making a reference to workers at the house:

"I asked the roofer guys if they had seen him, and they were just like 'Who?'" said Brad.

But something felt off about Brad's story, and it was about to become just that -- a story. The roofing contractor said none of his crew ever laid eyes on Chase.

"Nobody that was working for me or that was with me ever saw him," said the contractor, Brandon Duck.

In response, Brad said: "I mean I just assumed they had saw him leave, like, I don't see how they wouldn't have."

Chase's mom became convinced Brad Clement killed her son. She even theorized he disposed of Chase's body in a Dumpster. Brad says it would have been physically impossible, since at 6' 2" Chase was such a big guy.

"For me to just try to like roll Chase around and throw him in a Dumpster, like, in my front yard, like, I don't even think I could do it. Like, you know, without the help of somebody else," Brad said on Nancy Grace.

And there was no evidence that Dumpster was emptied into a landfill before anyone thought to search it.

"I don't think that he is alive. Because I don't think that he would stay away from us," said Amanda Massner.

Days turn into weeks, and weeks turn to months, and the "missing" case of Chase Massner goes ice-cold.

"Living the last three years with the not knowing and without him here, is pure hell," said mother Stephanie Cadena.

But then Chase's story captures the attention of the media and sparks the interest of Nancy Grace, catapulting the case into the national spotlight.

Where in the world is Chase Massner? After three years of searching, the case goes cold, filed away in the archives of the Cobb County Police Dept.

But there is one person who could shed light on the unsolved mystery: Chase's friend, Brad Clement.

"As far as I know, I was the last person that that's spoken to him," said Brad Clement.

Cops interview Brad Clement, but never name him a suspect. Frustrated, Chase's wife and his mother form "Team Chase," a group devoted to continuing the search as he remains missing for three years.

Then a tiny glint of light sparks at the end of a very dark tunnel. Their efforts capture the attention of the national media and Nancy Grace, blowing the case wide open.

Now with Nancy on board, the investigation picks up speed. She and Crime Watch Daily affiliate CBS46 arrange a dramatic face-to-face meeting between Chase's mother. And the one person who could know more about what happened to her beloved son. At that meeting Stephanie sits nervously across from Brad, desperate for any information about her missing son. Then Nancy Grace uses an audio recorder to capture the discussion for her podcast.

Cadena: "Can I ask you something?"

Clement: "Sure."

Cadena: "Did he say anything about me?"

Clement: "Not really. I think he said he'd, like, left your house or something for --"

Cadena: "He had stayed with me for three days."

"Stephanie wanted to believe Brad, but at that point she was not convinced that he was telling the truth," said WGCL-TV Reporter Daniel Wilkerson.

No clues to Chase's whereabouts come from the meeting -- another road block after years of suffering.

But then some good news: The case is transferred from the Cobb County Police Dept. to the D.A.'s cold-case unit, where a group of retired detectives take a closer look. And it's not long before the cold-case unit gets a game-changing tip, pointing in the direction of Brad Clement's former house, where Chase was last seen alive.

Now, many years later there's more manpower on the case, in the form of man's best friend. The K9 unit sniffs out areas the police initially overlooked.

"Based upon the information that we received several years ago," said dog-handler Tracy Sargent. "We did not search these areas. This is the first time we've searched it with the dogs."

Disappointingly, inside the house the dogs come up empty.

"The whole house has been checked with two dogs," said Sargent.

Then they reach the back yard.

"We had two dogs work. They both consistently responded in the same area," said Tracy Sargent.

K9 unit dog "Drako" frantically sniffs around -- and then sits down. Drako zeroes in on something buried under the dirt.

"It doesn't say that Chase was here, or something happened here with Chase," said Sargent. "It simply tells us that the dogs are indicating to human-remains scent."

Investigators get a warrant to dig up the dirt, where they make a chilling discovery. Beneath the deck, under a slab of concrete, in the exact spot where the dog sat is what's left of a body.

"I got a phone call. I understood what it meant, but never imagined in my wildest dreams that it would be Chase," said Chase's mother Stephanie Cadena.

But will the autopsy results reveal the grim truth that eluded everyone for all these years? With the horrifying discovery, it's time for cops to pay Brad Clement a visit. The lead investigator finds him at his mother's home and tells him they found a body. Brad freaks out and makes a frantic call to CBS46, insisting he's been framed.

Daniel Wilkerson: "You're trying to say that someone planted the body there?"

Brad Clement: "Well [---], I didn't put it there. I mean, well, I don't know how the [----] it would get there. It was a big [---] yard."

But finally after weeks, the body is identified. It's Chase Massner.

"I always tried to think of where he was or what happened. Never would have thought that he would be in Brad's back yard," said Stephanie Cadena.

And now Brad Clement is about to face another meeting -- with a jail cell. He first agrees to turn himself in, but never shows up, instead making a run for it. U.S. Marshals and the fugitive unit join forces in a multi-agency manhunt. Chase's mother pleads for the public's help to find the man she claims murdered her only son.

On a tip, six days later, cops track Brad down at a local supermarket just a few miles from his mother's house.

"Officers find Brad in the back of a U-Haul. Apparently he rented it, didn't take it back in time, and so the U-Haul Company notified the authorities," said reporter Daniel Wilkerson.

When Brad Clement exits the market, marshals close in. Caught on camera, Brad is lying on the ground in the pouring rain next to the U-Haul he was reportedly living in, barefoot with hands cuffed behind his back.

For Stephanie Cadena, even the arrest does little to ease her pain.

"Regardless of whether there's been an arrest made, it's not going to bring my Chase back," Stephanie said.

Brad Clement is whisked off to jail and charged with concealing a body.

The autopsy results do not reveal how Chase died. In fact, the coroner writes: "evidence of lethal trauma was not identified in the assessable soft tissues or the skeletal remains." The report also reveals this shocker: Chase had both morphine and methamphetamine in his system at the time of his death.

Chase Massner's body was found wrapped in a black tarp with packing tape around his chest and legs. Cops are hoping that tape may contain fingerprints that could point to Chase's killer.

Now faced with the reality of her son's death, Stephanie gets sick to her stomach when she thinks about her last meeting with Brad Clement.

"I don't understand the mindset of somebody that would look me in the face and know what he did with my son," said Stephanie.

At his first court appearance Brad Clement did not enter a plea. There is no known motive at this time.

At the very least, the Massner family can turn the page on what is a very dark chapter in their lives and remember the man they love.

"Now it's time to give Chase a proper funeral and begin to move forward in life, and remember the 26 happy years that we had with Chase," said Chase's mother Stephanie.