Calgary police have charged a 22-year-old man with five counts of first-degree murder in the stabbing death of five people.
The suspect, Matthew Douglas de Grood, is the son of a senior officer with the city police force.
Chief Rick Hanson says de Grood is a student at the University of Calgary and was an invited guest at a house party celebrating the end of the school year.
Police allege the suspect arrived at the party early Tuesday morning, got his hands on a large knife and began stabbing the victims one by one.
Three men died at the scene, while another man and a woman died in hospital.
``This is the worst murder, mass murder, in Calgary's history,'' Hanson said. ``We have never seen five people killed by an individual at one scene. The scene was horrific.''
Hanson says the dead were all ``good kids'' who were in their twenties.
Police were called to the northwest residential neighbourhood of Brentwood, not far from the University of Calgary campus, at about 1:20 a.m.
The suspect was arrested with the help of the police canine unit about 40 minutes after the stabbings. He was taken to hospital for treatment of dog bites.
Hanson says the suspect worked at a grocery store and his father had worked with the force for 33 years. There was no immediate word about a possible motive.
The blue-sided house where the stabbing took place is on a quiet, tree-lined residential street. It was surrounded with yellow police tape as medical examiner staff brought three bodies out on stretchers.
Neighbours in the area say the house was being rented by University of Calgary students and the party stemmed from the student union's annual Bermuda Shorts Day, which was held Monday.
The event, shortened by students to BSD, is an annual outdoor party on campus featuring live music and beer gardens to celebrate the end of classes.
The school's student newspaper, The Gauntlet, wrote about the tradition two weeks ago in a story titled ``BSD: It'll be a bloodbath.''
On Twitter, many students wrote about how they starting drinking early in the morning Monday and continued after the campus event at parties elsewhere.
Trent Pattison wrote: ``Sad that days that are supposed to be remembered as a fun great day will be remembered for the wrong reasons. BSD2014.''
The university posted a short statement about the deaths on its website, saying counselling would be offered to anyone needing it.
``The University of Calgary is mourning the loss of five young people killed early this morning in Brentwood,'' the statement reads.
``The identities of the deceased have not yet been confirmed by Calgary Police Services. Once details are confirmed by Calgary Police Services, the university will provide a further statement.''
Calgary Mayor Naheed Nenshi took to Twitter to offer condolences.
``Thoughts and prayers of all Calgarians are with the young people we lost this morning, their families, friends, and university community,'' the mayor said.