Alvin and Kathy Liknes had just wrapped up an estate sale at their home in Calgary, Alberta in Canada in June 2014. But soon the couple and their 5-year-old grandson became the center of a massive search.

Inside a quaint house nestled on a quiet street, a scene so grisly, so gruesome, it defies comprehension, a murder case that gripped a nation and made headlines around the world.

Jennifer O'Brien, a busy mom with three young boys, went to pick up her 5-year-old son Nathan from his grandparents' house in Calgary, Alberta in Canada. But when Jennifer arrived, she stumbled upon an odd scene: The front door was already open, and as she walked in, she's hit first with the smell of death.

And then, pools of blood everywhere and no sign of her parents or son.

"There was blood all over the beds, on the walls, on the floor," said Calgary Herald Reporter Bill Graveland. "There were bloody footprints in the hallways. There was drag marks, like something had been dragged through pools of blood."

And the most heartbreaking sight imprinted on a wall.

"There was a little hand print on the way out as if a little boy was being dragged along and had put his hand against the wall to brace himself," said Graveland.

Bill Graveland says Jennifer O'Brien, hysterical, calls police, telling them: "I think my family has been killed."

"They told her to stay in her car with the doors locked because they were afraid there could potentially, might be someone still in the house," said Graveland.

Cops bust into the gruesome scene and feverishly search the house, but no bodies are found. The grandparents and little Nathan are missing.

At the scene, there is not one shred of DNA found, not one fingerprint from a potential killer.

Cops immediately issue an AMBER Alert in hopes of locating the family. Hundreds of police search relentlessly but with no sign of Nathan and his grandparents.

They eventually circled back to the scene of the massacre, holding onto any sliver of hope to locate the 5-year-old alive.

"They hoped maybe he saw the violence and had hidden somewhere. So they went through all the closets, under the beds, anywhere anyone could hide," said Bill Graveland. "He wasn't there."

Nathan O'Brien, an adorable blonde mop-topped boy, was the spirited middle child of three brothers in the close-knit O'Brien clan. He loved superheroes and made friends wherever he went.

The grandparents, Alvin and Kathy Liknes, were the glue that held the family together.

"My mom was my best friend. She was just a very caring, loving mother who made a home for all of us," said Jennifer O'Brien. "My dad, he was an entrepreneur who was always trying to start up a business and be successful and he was."

Alvin and Kathy were about to start a new chapter in their lives -- retirement -- on the day they disappeared. They were having an estate sale, downsizing after buying a new home in Edmonton.

"The police went on for a couple of weeks where they were still hoping that they would might find them held somewhere, and that perhaps the injuries that were sustained in the home weren't fatal," said reporter Bill Graveland. "They searched for a couple of weeks looking for them and never found any bodies."

And it became very obvious this was no abduction -- more likely it was a triple-murder, with a violent killer still on the loose.

The trio disappeared after Nathan had slept over at Alvin and Kathy Liknes' house.

Within days, more than 1,300 tips pour in -- so many that it crashed the police department's computer system.

Cops analyze hundreds of hours of surveillance tape. Then something suspicious catches their eye.

"They went to all of these homes in the neighborhood and they found this green mid-'70s Ford F-150 truck. Very distinctive looking," said reporter Bill Graveland.

Police release a flyer with a picture of the green pickup truck spotted on the grandparents' street the night they disappeared. And it wasn't long before cops get a call from a woman who said she recognized the truck. It belonged to her brother.

The owner of that truck is a man named Doug Garland, and police now want to talk to him. They nab him at a traffic stop and hold him in jail on a previous false-identity charge.

"He was always very quiet and didn't reveal anything to police," said Graveland.

Meanwhile, Canadian Mounties storm the 40-acre farm where Garland lives with his elderly parents in an emergency hostage rescue -- but no one was found.

But there was something. One of the first things they notice was a burn-barrel smoldering near a greenhouse. Inside the tank, nothing but ash.

"There's no blood, there's no sign of any evidence," said Graveland.

Back at police headquarters, Garland was released on bail and given strict instructions not to go back to the farm. In the meantime, cops secure a warrant and scour every inch of the sprawling property.

Hidden away in basement rafters, police find a computer hard drive with reams of painstaking research on gruesome and violent topics on it.

"He downloaded a bunch of things, things like attack your victims at like 3 o'clock in the morning, the element of surprise. Painful ways to torture," said Graveland.

Cops say the hard drive was also littered with images of his alleged sexual obsessions.

"He had quite a fetish about adult diapers, and there were a number of pictures of men and women being restrained, perhaps killed, wearing adult diapers," said Graveland.

Every inch of the place was searched, including the basement office, with a library of the macabre.

"One was a book on how to poison people," said Graveland. "Another one was called the 'Joy of Killing.'"

Also in the basement: a cross-dresser's fantasy.

"The set of prosthetic breasts, the two long blonde women's wigs that were on these mannequin heads," said Graveland.

Racks of women's clothing in Garland's size, and a vast collection of shoes: 89 pairs of men's and women's shoes in Garland's size, according to Bill Graveland.

Missing from and empty shoebox was a pair of size-13 Doctor Scholl's brand tennis shoes.

Then, cops seized boxes filled with weapons: handcuffs, some in a child's size; hacksaw blades; leather straps; bone saws; knives; guns; and a straitjacket.

But investigators don't find bodies.

Of all the disturbing clues, one stood out: The smoldering burn barrel. Cops had noticed it during the first search of the farm. This time investigators took a closer look, and sifting through the ashes they find a baby tooth.

"They found the burnt flesh and a lot of the bone fragments in the embers of the burning barrel," said Graveland.

Not long after collecting evidence, cops soon learned that Garland was no stranger to Alvin and Kathy Liknes -- they actually had a layered and complex relationship that went back years.

Garland's sister Patty -- the one who reported the truck -- is married to the Liknes' son.

But the detail that sparked cops' interest is that Alvin, a successful entrepreneur, had employed Douglas Garland years before.

"Patty's husband had suggested that when Alvin Liknes was looking for someone to work with that Doug would possibly be a good choice," said Graveland. "He had some education, and he was fairly handy, and he wasn't doing anything."

The two men worked on a pump invention together, but the project never went anywhere, and Liknes eventually fired Garland.

"They worked together on building a pump for the oil-and-gas sector," said Graveland. "The brains was Alvin Liknes, and it was his invention. It never made a penny, it never got used. But apparently Doug Garland was angry and bitter over it for years."

Bitter enough for murder? While mountains of incriminating evidence are piling up and more intelligence on Garland's history with the couple is gathered, cops are keeping a close eye on the 57-year-old Garland, following his every move.

He is recorded on surveillance camera at an auto parts store buying what looks like circular-saw blades. Police are especially interested in what he's wearing: On his feet are the same Doctor Scholl's missing from the shoe box. Do they match blood-soaked prints found at the grandparents' home?

"They actually have a shoe database, federally in Canada, and they matched it to a Dr. Scholl's running shoe, and were able to trace it to a certain style," said reporter Bill Graveland.

Even though no bodies are ever found, with 1,400 pieces of the most grotesque evidence imaginable, cops have enough to make their move. But so did the crazed killer.

Investigators had Doug Garland under surveillance after their first search of his property. Then two weeks after Nathan and his grandparents disappear, cops catch Garland trying to sneak back on the farm where he lived.

"The belief was that he was trying to get rid of maybe a little more evidence," said Bill Graveland.

The sadist didn't get far.

"They cornered him, because the helicopter could see him and he finally surrendered," said Graveland. "They told him 'Don't make this even any worse than it already is,' and he came out and laid down on the grass and they handcuffed him."

Doug Garland pleaded not guilty to three murder charges. The sensational five-week trial transfixed a spellbound nation.

In opening statements, prosecutors told the three-woman, nine-man jury that Garland held a years-long grudge against Alvin Liknes over a patent for a pump.

On the day they disappeared, Alvin and Kathy were having an estate sale since they were planning to move and wanted to downsize. So Garland put his sordid plan into action.

The first step: breaking into the couple's home.

"It appeared Mr. Garland had drilled a hole in one of the locks," said Graveland.

The murderous timeline unfolded from there. Once in the house, Garland preyed on his victims. According to his meticulous and obsessive research, 3 a.m. was the best time to attack.

"Mr. Garland went into Alvin Liknes's bedroom and bludgeoned him, then he went to the next room where Kathy Liknes was sleeping with her grandson," said Bill Graveland.

Was little Nathan just collateral damage, or was he also a target?

"I don't believe he was a target, but he decided he didn't want to leave any witnesses," said Graveland.

Forensic experts believe the family was alive when Garland dragged them from the home and shoved them in the truck.

"They have pictures of what appeared to be a white sheet in the back of the truck and the police believe that's where the bodies of the three were," said Graveland.

Shockingly, even with all of the bloodshed, none of Garland's DNA was ever detected at the house.

"He did a lot of research on how to not leave DNA evidence," said Graveland. "There were a number of these white suits that the forensic people wear when you see them on TV shows. They believed that he was wearing those."

Then Garland drove about 20 miles to his parents' rural farm, where unspeakable horrors awaited. Nathan and his grandparents' DNA were found on instruments of torture, like meat hooks, bone saws and knives.

"They found Kathy Liknes's DNA on [a meat hook]. They found Alvin Liknes and Nathan O'Brien's DNA on the meat saw. And they found DNA from all three victims on the outside of a pair of rubber boots," said Graveland.

But even with mountains of blood and fragment evidence, no bodies were ever found.

"There was no one that actually saw the deaths. There was nobody that saw Doug Garland kill them and they don't even have a cause of death on these people," said Graveland.

Incredibly, Garland's elderly mother took the stand against her son, testifying that she didn't hear him leave home the morning the three disappeared.

"She actually had found out they were missing, mentioned it to him and he said, 'I don't want to talk about that.' He already knew," said Graveland.

Perhaps one of the most disturbing images presented at trial were pictures taken, completely by chance, from a mapping plane that flew over Garland's property the day after the family disappeared.

"Five or six months later he's going through the photos and he discovers the Garland farm," said Graveland. "He can see what appears two headless torsos of adults. Looks like they're laying face-down, wearing diapers, and a small figure in the grass next to them, which is, they believe, was Nathan O'Brien, right by the burning barrel."

In this case, the dead speak volumes.

"There were no bodies," said Graveland. "Only tiny little pieces."

The only proof of their existence on the planet was buried in the ashes left behind in the burn barrel.

"That is where they found one small piece of flesh, which could have belonged to Alvin Liknes. Bone fragments were from a 5-year-old boy. So he burned everybody, apparently," said Graveland. "Chopped them up it looks like, and then burned the bodies, just cremated them."

While the gruesome details of the heinous crimes unfold in court, Doug Garland appeared unfazed.

"He sat through the first round of hearings and the second taking notes," said Graveland. "We never heard a denial, we never heard an 'I'm sorry.'"

None of the victims' families took the stand, but Nathan's dad's written words reverberated through the courtroom:

"Rod O'Brien, when he did a victim impact statement, basically said that 'I didn't even have enough of my son to bury. There was not enough left of him,'" said Bill Graveland.

Then after weeks of traumatizing testimony and about 10 hours of deliberation, Doug Garland was convicted of first-degree murder in all three deaths. Garland received three consecutive life terms for his heinous crimes.

"Nathan's spirit certainly lives on. It lives on in this community," said Jennifer O'Brien.

They are coping day to day raising their two boys, and by creating The Nathan O'Brien Children's Foundation, funded in part by a $1 million donation from an anonymous donor.

"Nathan loved sports, so we have an annual decathlon where we have children come out and learn how to play hockey," said Jennifer. "He would have loved to have been part of that right? So it just makes sense for us to do that for other children and other families."

"Every time somebody says something with a warm kind word or kind heart, you know, and sometimes they feel uncomfortable because they don't want to say it to us because they're scared they're going to get us upset," said Jennifer. "And I just say thank you, thank you for saying that to us, and thank you for praying for us, and thank you for showing us that you care. Because it means the absolute world."

One of things Nathan loved was nighttime talks with his dad at bedtime. And one conversation will forever linger in Rod's memory.

"Nathan had started asking me at night time what heaven was like, which is kind of a strange question coming from a 5-year-old," said Rod. "And I would say, 'Well, you can fly around in heaven like a superhero,' 'cause Nathan loved superheroes, 'there's no night times, you can play all the time.' He goes 'Well, I'm gonna welcome you into heaven, dad, you guys."