WARNING: The following report contains graphic details that some may find disturbing.

It was a dramatic first day in court for the trial of Matthew de Grood, the 24-year-old man charged with five counts of first-degree murder in connection with the stabbing deaths of five young people at a Calgary house party.

Families of the victims heard graphic details Monday of how the accused told police he believed he was killing Medusas and werewolves in the name of God and believed the deaths were “justified.”

De Grood has pleaded not guilty to five counts of first-degree murder. However, he admitted in an agreed statement of facts that he stabbed the five young people to death.

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The trial started on Monday, more than two years after the stabbing attack occurred at house party several blocks from the University of Calgary campus.

Police say the April 15, 2014 attack is Calgary's worst mass killing.

Officers called to the scene said they discovered three men already dead. A fourth man was found stabbed on the lawn, and a woman was found wounded inside the house. Both later died in hospital.

The victims were later identified as Lawrence Hong, 27; Josh Hunter, 23; Kaitlin Perras, 23; Zackariah Rathwell, 21; and Jordan Segura, 22. All were students at local universities and colleges.

The agreed statement of facts said that de Grood's family began noticing a change in his behavior in the weeks prior to the attack.

The suspect began talking about politics and religion, and making erratic posts on Facebook and in text messages to family members and co-workers.

The statement of facts said he was not seen consuming alcohol or drugs at the house party. De Grood had just finished a shift at a grocery store and wore his uniform to the party. Once he arrived, De Grood put on a pair of blue latex gloves, according to the documents.

A childhood friend told police that de Grood was acting unusual and made strange comments, including: "Obama was the antichrist."

The statement of facts said the stabbings occurred shortly after de Grood had a conversation with Rathwell about Buddhism.

"I asked him to give me my space. We were walking toward the knife block, so I decided to shoot first because I didn't know what he was going to do so I stabbed him," de Grood is quoted as telling police officers.

"Then the people on the couch saw and obviously started freaking out, so I killed them from left to right as quickly as I could. The girl ran into the corner so I went and stabbed her. I said I'm sorry I have to do this. Then the guy from the kitchen wasn't dead. I had to hunt him down. Then I just left."

When police arrived and arrested de Grood, he told officers that he was trying to kill the victims before they killed him. He also said other strange things, including that he was an alien, that he was born in an incubator and that he believed he was Jesus.

According to the agreed statement of facts, de Grood told police he stabbed the victims to death.

"I just want to say that when I stabbed them, I tried to do it mercifully. I aimed for their heart. They put up a struggle, which made it hard but, so you know, it wasn't sadistic or anything," de Grood is quoted telling police officers.

"What I did may seem atrocious but I was killing Medusas, werewolves.”

He told officers he wanted the cheapest and worst public defender, according to the statement of facts.

A police official from the K-9 Unit told the court Monday that de Grood did not react to any pain after a police dog bit his right arm.

Several witnesses were called to the stand Monday, including police officers and de Grood’s former boss. The assistant manager of a grocery store where de Grood worked said the accused was typically “an all-around good person” but “wasn’t himself” the month of the stabbing.

The manager shared text messages with the court sent from de Grood on the day of the attacks. The messages included "Trust that I never hurt anyone," "All will be known," and "5.”

Text messages from de Grood’s mother, who wrote to her son on the day of the killings, were also read in court. "Matt you are not making sense I need to talk to you now," she wrote.

Victims' families issue statement: 'The grieving and the memories never end'

Before the trial started on Monday, Gregg Perras, father of Kaitlin Perras, read a statement on behalf of all of the victims' families.

"We are here to represent the voices of the victims, our loved ones who had their futures taken away and who cannot represent themselves," he said tearfully from outside the courthouse.

Perras described the past two years as "extremely difficult, incredibly long, and anxiety ridden," but said the families were thankful for the support they've received from friends, family members, and the greater Calgary community.

"The grieving and the memories never end for us. There's no such thing as a new normal that some people talk about. There is only existing, surviving, and a series of bittersweet events going forward in our families' lives, such as graduations, weddings and grandchildren.

"These milestones will be happy and they will be sad."

Perras asked the media to respect the families' privacy throughout the trial, as they focus their attention on their loved ones who died in the attack.

"All we ask is that you remember how they lived: full of purpose, full of life, full of goodness, and love for their friends and family," he said. "Their deaths and this tragedy do not define them."

An out-of-town judge will be hearing the trial at the request of both the prosecution and defence. This is because the accused's father is a high-ranking Calgary police officer who could be called to testify.

De Grood has been undergoing treatment at a forensic psychiatry centre since his arrest in 2014. He underwent a psychiatric review, and was determined fit to stand trial because he understands the charges against him, and is able to communicate with his lawyer.

The trial will resume at 10 a.m. on Tuesday.

With files from The Canadian Press, CTV Alberta Bureau Chief Janet Dirks, and CTV Calgary’s Ina Sidhu

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