The man accused of killing five-year-old Nathan O'Brien and his grandparents, Alvin and Kathy Liknes, in 2014 faced a judge and jury on Monday and the little boy's mother was the first to testify in the case.

Garland, 56, is charged with three counts of first-degree murder in the case that gripped the country two and a half years ago.

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The trial got underway at 10:00 a.m. in a Calgary courtroom and Garland's lawyer entered a 'not guilty' plea on his behalf.

Garland sat emotionless in the prisoner's box, wearing a blue jumpsuit.

Justice David Gates instructed the jury at the beginning of the trial to avoid all media reports as the "case has generated a large amount of public interest". He also warned the jury that the evidence and testimony presented during the trial may be 'distressing or disturbing' at times.

A jury of 14, plus two alternates, was selected last week to hear the case.

Crown prosecutor Vicki Faulkner said in her opening remarks that the murder was a deliberate act planned because Garland held a petty grudge against Alvin Liknes over a pump patent.

Garland had a plan that he 'meticulously researched' and documented on a hard drive that was found hidden in a barn on the property owned by his parents.

The Crown says the hard drive included extensive research by Garland on how to commit a murder, social media data on the Liknes' and maps of their home.

Faulkner said that the victims were forcibly taken from their Parkhill home and killed at the Garland acreage, just outside of Airdrie, and that their bodies were burned in a burn barrel.

Court heard that DNA from Nathan and Alvin was found on a saw and DNA from Kathy was found on a meat hook. Both tools were found on the Garland farm.

The Crown says that Peregrine, an aerial photography company hired for mapping services, conducted an aerial survey at the beginning of July 2014 and inadvertently captured images of the bodies of Nathan, Alvin and Kathy at the farm.

Faulkner said that on June 30, 2014, Jennifer O'Brien, Nathan's mother, went to pick up her son and found the inside of the home covered in blood, with spatters on the walls and carpet.

The Crown wrapped its opening statement by telling the jury what it intended to prove over the course of the trial.

"What you the jury will see, is that, Douglas Garland is an obsessive and methodical planner, who planned and deliberately killed Alvin Liknes, Kathryn Liknes and Nathan O'Brien."

Jennifer O'Brien, Nathan's mother and Kathy's daughter, was the first to testify saying that she and Nathan had a good relationship with Alvin and Kathy.

She said she had gone to her parent's home on June 29, the day of their estate sale, with her two sons Nathan and Max to help out as the Liknes' were selling their home and moving to Evansburg, Alberta.

O'Brien told the court that her son Nathan wanted to sleep over at his grandparent's home and she agreed.

At about 11:00 p.m., O'Brien's one-year-old son Max became fussy and she decided to take him home, leaving Nathan in the care of her parents.

In the morning, O'Brien said she found it strange that her mother hadn't called her and didn't answer the phone when she called.

When she arrived at her parent's home to pick Nathan up, she found the side door had been left open.

"I immediately saw pools of blood and thought 'there is something really wrong here'," she told the court.

She was unable to locate the trio and left immediately, calling her husband to tell him what she saw.

"My family's been murdered and they've taken the bodies," she told the court.

On Monday afternoon, Allen Liknes Jr., Alvin's son took the stand and said that his dad did not have any personal loans or debts to pay, to his knowledge. Under cross examination, he said he believed his dad and Garland had a falling out in 2007 but that there were never any threats.

Family members of the victims told the media last week that the pain of their loss hasn’t eased since the murders.

In a statement released last Thursday, they wrote:

It has been two and a half years since Nathan, Alvin and Kathy were taken from us. Our pain has not lessened during this time.

The next five weeks of this trial will be very difficult for us. We can only hope that at the end of this grueling time we will find justice for Nathan, Alvin and Kathy.

We are grateful for the overwhelming support we have received from people in Calgary and across the country.

Before the trial started, Garland's defence lawyers expressed concerns about the publicity of the case affecting the fairness of the trial, but say the jury selection process helped alleviate those issues.

“There’s been a lot of publicity, which is why we had the challenge for cause on jury selection. But, as for preparation on the case, it hasn’t had any impact,” said Kim Ross.

On Tuesday, Douglas Garland's parents and sister are expected to take the stand.

The trial is scheduled to last five weeks and the Crown is expected to call 60 witnesses to testify, including family members, police and forensic experts.