For the latest developments, see Tuesday's story: Douglas Garland's family to testify for prosecution on Day 2 of triple murder trial

You can also follow the trial via Meghan Grant, the CBC's reporter in the courtroom, who will be livetweeting the proceedings. On mobile? You can see the live blog here.

The man accused of killing a Calgary couple and their five-year-old grandson was motivated by a "petty grudge" over a patent dispute and burned their bodies in a barrel after killing them, court heard Monday as the triple-murder trial of Douglas Garland began.

In her opening statement, Crown prosecutor Vicki Faulkner said Douglas Garland was angry with Alvin Liknes over a dispute relating to a patent for a pump that dated back years.

She told the jury that when Garland learned through internet searches that Alvin and his wife, Kathy Liknes, were planning to leave Calgary, Garland finally decided to act on his grudge.

Five-year-old Nathan O'Brien was at his grandparents' home, having an impromptu sleepover, when the trio were taken.

Forensic analysis of Garland's computer hard drive will be presented as evidence, said Faulkner, showing research on murder, "how to kill without emotion," torture and autopsies.

Douglas Garland was angry with Alvin Liknes over a dispute relating to a patent for a pump that dated back years, the Crown alleged in an opening statement Monday. (CBC)

Garland, 56, is charged with three counts of first-degree murder in connection with the missing family members who were last seen June 29, 2014.

Evidence 'all over' rural property

He said "not guilty" in a loud, clear voice when asked for a plea at the outset of his trial.

The trio's disappearance made national headlines as Canadians held out hope for two weeks that they would be found alive.

Following a massive search and investigation involving hundreds of police officers, that hope was dashed on July 15, 2014, when Garland was arrested and charged with murder.

Jurors heard evidence was later found "all over" a rural property just north of Calgary, where Garland lived with his parents.

Nathan is shown in this family portrait hugging his older brother. The boy opted to sleep over with his grandparents on the last night he was seen alive. (Facebook)

The Crown said DNA evidence from the missing family members was found on a saw and meat hooks, and bones and a tiny tooth were discovered in a large burn barrel.

A mapping plane that flew over the property also took photographs that show three bodies in the grass, according to the Crown's opening statement.

Alvin and Kathy were lying face down, according to the prosecution.

"You will also see a small figure curled up on the grass," said Faulkner. "The Crown says this is Nathan."​

Impromptu sleepover

Jennifer O'Brien was the first witness called at the trial.

She testified that on his last day alive, Nathan was given the option to visit the zoo or his grandparents, and he chose his grandparents — who were planning to move to Edmonton and spend much of their time in Mexico.

Once at their home, Nathan's "proud" grandfather, Alvin, took the boy to the playground.

"He was just truly a kind, loving, happy, happy boy," Jennifer said of Nathan.

About 30 people attended an estate sale held by the the family that day. Once everyone cleared out, the family ordered Chinese food and watched a movie together.

"We just sat there and enjoyed each other's company," said Jennifer, who described her mother as her best friend.

A sketch of the courtroom during the first day of Douglas Garland's triple murder trial Monday. The main courtroom was packed and an overflow courtroom was also full. (Janice Fletcher)

Nathan asked if he could stay for a sleepover that night at his grandparents' house, and Jennifer and her youngest also decided to stay, according to her evidence.

But when the one-year-old woke up in the middle of the night, she scooped him up and drove home, leaving Nathan sleeping with his grandmother.

The next day

On the morning of June 30, Jennifer woke up, got the baby ready and called her mother, but Kathy didn't answer.

When Jennifer walked into her parents' home with her one-year-old son perched on her hip, she said she knew right away what happened.

"My family's been murdered and he's taken the bodies," she told her husband as she walked around the bloodied home.

She said it was a "bloody scene" inside, with blood on the beds, walls and in the kitchen.

"I immediately saw pools of blood and hand marks of blood on the wall."

When Jennifer O'Brien arrived at the Liknes home to pick up her son, she found blood throughout the house. Here, a photo of one of the bedrooms that was among the evidence submitted. (Court exhibit)

Alvin and Garland's relationship sours

Alvin Liknes's son, Allen Liknes, was the prosecution's second witness. He was married to Douglas Garland's sister Patti at the time the family disappeared.

Both Allen and Patti were instrumental in alerting police to information that caused Garland to become a suspect the day the trio was discovered missing, according to the Crown's opening statement.

Allen testified that he, Alvin and Garland had worked together around 2006-2007, when his father hired Garland to do some wiring for a pump the father and son were developing.

The relationship between Alvin and Garland disintegrated beginning in 2007 when Garland became upset that he had been let go from the business after he stopped answering the phone, Liknes testified. By 2010, Allen testified that he and his father stopped talking to Garland because Alvin had had enough.

Allen told officers about the long-standing grudge Garland held against Alvin on June 30, 2014.

The same day, Patti Garland recognized a photo of a green truck released by police as similar to the one driven almost exclusively by her brother, Douglas Garland. The image had been captured by a surveillance camera on the Liknes's street the night the family disappeared.

She sent a photo to Allen who forwarded it on to police, according to the Crown's opening statement.

In cross-examination, Allen Liknes told defence lawyer Kim Ross that Garland never threatened his father.

"He's not confrontational at all," said Allen Liknes. "If anything he's sneaky."

Jim Lutz and Kim Ross represent Douglas Garland. They have not said if they plan to call any witnesses during the trial. (Meghan Grant/CBC)

Trial fills 2 courtrooms

The main courtroom where the trial is taking place was full on Monday, with seating reserved for victims' and the accused's family as well as media.

Every seat in a second overflow courtroom was also full.

Court of Queen's Bench Justice David Gates and a jury of 14 people will hear five weeks of evidence.

"It's been a long process for all parties involved, so we're happy to get it moving," said defence lawyer Kim Ross.

Crown prosecutors Shane Parker (pictured) and Vickie Faulkner estimate they will call about 60 witnesses. (Jeff McIntosh/Canadian Press)

The victims' families are apprehensive, but hopeful.

"The next five weeks of this trial will be very difficult for us," reads part of a statement they released.

"We can only hope that at the end of this gruelling time we will find justice for Nathan, Alvin and Kathy."

The families say they will not be speaking again before or during the trial, and have asked for privacy during "this incredibly stressful time."

Prosecutors Shane Parker and Vicki Faulkner expect to call about 60 witnesses.

It's unknown whether defence lawyers Kim Ross and Jim Lutz will call any evidence.

"That's a decision we'll make at the close of the Crown's case," said Ross.