The families of Nathan O'Brien and his grandparents, Alvin and Kathy Liknes, say hearing the details of how their loved ones died during the trial of the man accused of killing the three family members has been very difficult.

"The last five weeks have taken a heavy toll on us," family members said in a written statement released Monday. "It has been unbearable for our family and friends to endure the gruesome details that have been presented throughout the trial."

Douglas Garland, 57, is charged with three counts of first-degree murder in the deaths of five-year-old Nathan and his grandparents, Alvin, 66, and Kathy Liknes, 53, of Calgary.

"Nothing will bring Nathan, Alvin and Kathy back to us, but we can only hope the court will see justice done in their names," reads the statement.

Crown lawyers Shane Parker and Vicki Faulkner, as well as defence lawyers Kim Ross and Jim Lutz made closing arguments to the jury on Monday.

Douglas Garland was found guilty of three counts of first-degree murder Thursday in the deaths of Kathy Liknes and Nathan O'Brien, left, and Alvin Liknes, right, in June 2014. (Calgary Police Service)

Jurors had heard earlier in the trial that Garland was angry at Alvin Liknes over a business relationship formed and broken years earlier.

"[Nathan] had not even been born yet when Alvin and Garland had a falling out," Parker said Monday. "He neither forgave nor forgot. He stewed.

"You cannot leave a witness; once Nathan witnessed the attack of Kathy in the front bedroom, he had to be killed."

Defence lawyer Ross reminded jurors there was no evidence presented that his client was ever inside the Liknes home.

"Not a single piece of DNA," said Ross. "Not one drop of blood, no saliva, not one strand of hair, no skin."

Garland is entitled to the presumption of innocence, Ross said.

"It is our submission … that the Crown has failed to prove Douglas Garland caused the death of Alvin Liknes, Kathryn Liknes and Nathan O'Brien," said Ross.

The defence team did not call any witnesses to testify.

'They were always going to die by his hand'

For Garland, the killings were all about domination, Parker said earlier in the day. He told the jury there is no doubt that Garland murdered all three family members.

He said Garland was researching the Likneses and methods of killing on his computer starting in 2013, but when he learned the couple planned to move away he decided to take action, said Parker.

Internet searches found on a hard drive that had been hidden in the farmhouse where Garland lived with his parents showed be planned to break into the home of the man he hated, according to the Crown.

The plan "intensified" in March 2014 with dozens of searches and documents stored on the drive. Things like "How to Kill Without Joy," research on weapons, torture, the Likneses, their address and how to pick the exact lock that was found tampered with on their side door.

"They were always going to die by his hand," said Parker. "All phases of capture and death were planned and researched from beginning to end."

Nathan wound up having an impromptu sleepover with his grandparents on the night of June 29, 2014.

Surveillance video gathered from area homes and businesses show an older model green pickup truck, just like the one Garland drove, parked on the Liknes's street in the early hours of June 30.

After about 90 minutes, the truck was seen driving off with a large white object inside the truck bed — the Crown claims that it was the boy and his grandparents.

The photo on the left shows what the Crown says are three bodies covered by something white in the bed of Douglas Garland's pickup truck around 5:15 a.m. on June 30, 2014. Two hours later, the truck was spotted again, but it was empty. (Court exhibit)

"This was the transport truck," said Parker. "Nathan, Kathy and Alvin in these photos, are prisoners, being held against their will."

But the white item visible in surveillance footage gathered from homes and businesses is not covering the three victims, according to the defence.

"It's a fact; there are no bodies in that truck," said Ross. "Those people did not leave that house alive."

'Nathan was alive outside the bedroom'

The truck was spotted on CCTV footage again later in the morning, driving from the Airdrie area back to the Liknes's street where it rolled past the bloodied home and continued to 37th Street and 11th Avenue S.W. — the location where Garland had an appointment with a psychiatrist every Monday morning.

Less than two hours later, Jennifer O'Brien arrived at her parents' home to find the trio gone and the house covered in blood.

A small handprint formed from a mix of Nathan and his grandmother's blood was just two feet from the floor.

"Little Nathan was alive outside the bedroom," said Parker.

The Crown contends that the family members were killed on the farm, but the defence said they were killed inside the Liknes home, in a "very violent and fatal struggle," said Ross.

A portrait of the O'Brien family from Rod O'Brien's Facebook page. Nathan, second from right, hugs his older brother. (Facebook)

In what the Crown has called a "dumb luck," a mapping plane flew over the Garland farm on July 1 and took aerial photos of what appears to be two adult bodies laid out on the property near three sheds. A smaller, less clear figure is next to them.

"It's a devastating image," said Parker, while showing jurors the photo once again.

"This is as close as you get to an autopsy photo in this case ... These were living and breathing people; grandparents, a five-year-old with wonderful parents."

This is the area on the Garland farm where the Crown says three bodies could be seen in photos taken by an aerial survey company. (Court exhibit)

Two weeks after the search for Nathan and his grandparents began, it ended when Garland was arrested and charged with three counts of murder.

Parker also went over key evidence presented by the prosecution during the trial:

DNA from all three victims was found on the Garland farm, including on items the accused had recently purchased like a hacksaw and meat hook.

A small piece of human remains belonging to Kathy Liknes was found in the grass on the farm.

A fragment of Alvin Liknes's remains was found in ashes on the Garland property.

Kathy Liknes's DNA was found in Garland's truck.

Alvin Liknes's DNA was found on a shoe Garland was wearing at the time of his arrest.

The case will go to the jury on Wednesday afternoon after Court of Queen's Bench Justice David Gates delivers his final instructions. Jurors will then be sequestered until a verdict is reached.

In the statement issued by the victims' families Monday, they thanked the jurors. A sentiment echoed by Parker at the end of his submissions.

"You are faced with an awesome responsibility; the evidence in this case has been hard to hear, I'm sure of it," he said.

"Follow the law, follow the evidence. Don't outsmart your common sense."

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