Dustin Duthie, who is accused of murdering his girlfriend, mother and stepfather in Calgary in 2018, sobbed through much of the morning as his preliminary inquiry got underway Monday.

Duthie is charged with three counts of second-degree murder, accused of killing Taylor Toller in July 2018 and then his mother, Shawn Boshuck, and stepfather, Alan Pennylegion, a week later.

A preliminary inquiry is held to determine if there is enough evidence for the accused to stand trial. A publication ban protects any of the evidence from being reported in order to protect the accused's right to a fair trial.

Provincial court Judge Sean Dunnigan is presiding over the two-week hearing and will decide at the end whether to send Duthie to trial.

Dustin Duthie is charged with three counts of murder in the deaths of his girlfriend, Taylor Toller, his mother, Shawn Boshuck, and his stepfather, Alan Pennylegion. (From left: Taylor Toller's Facebook page/Shawn Boshuck's Facebook page/Supplied)

On July 31, 2018, Duthie was arrested after he called 911 to report the killings, according to police.

When officers responded, they discovered the bodies of Toller at her southeast apartment in Applewood Park and his mother and stepfather at their Hidden Valley home in northwest Calgary.​

There have been mental health concerns from the outset of the case with Duthie being held at times at the Southern Alberta Forensic Psychiatry Centre.

Prosecutor Shane Parker is expected to call more than 30 witnesses.

Duthie is represented by B.C. defence lawyer Ray Dieno.