Calgary police have formally announced murder charges against Douglas Garland, a day after concluding that a five-year-old and his grandparents, missing for the past two weeks, are dead.

The bodies of Alvin Cecil Liknes and Kathryn Faye Liknes and their grandson Nathan O'Brien have not been located. This makes the charges especially unusual, experts say.

"The preponderance of evidence is such that it has led our investigators to believe that they are dead," Calgary Police Chief Rick Hanson told reporters Monday. "Hence, two counts of first-degree murder, one count of second-degree murder."

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"It is safe to say that even as the days went by, there's always a hope. There's always a glimmer of hope," Chief Hanson said. "Unfortunately, with the laying of the charges, we've taken that hope away from the family."

Investigators made an arrest in the case at 1:30 a.m. Monday, near an acreage outside Airdrie, Alta. Mr. Garland, who police called a "person of interest" in the missing persons case, lived on this property, owned by his parents.

Mr. Garland is now charged with two counts of first-degree murder in the deaths of Kathryn and Alvin Liknes, and one count of second-degree murder in the death of Nathan O'Brien. His next court appearance will be on Wednesday, Calgary police said in a news release.

Officers called the case a "mystery" when they launched the investigation, and the most significant question – the location of the bodies – remains unanswered despite police pressing murder charges. Chief Hanson on Monday pleaded with landowners around Airdrie, where Mr. Garland lived with his parents, to search their properties for anything suspicious. He urged energy companies operating in nearby fields and pastures to be vigilant in looking out for anything unusual. Calgary Police Service members and RCMP officers have already combed through the Garlands's rural property, nearby swamps and a pasture. They also picked through two of Calgary's three landfills. More than 200 officers were assigned to the case and 900 tips came in, Chief Hanson said.

"This level of public support and engagement has never been seen in previous investigations of this magnitude," he said at the press conference. "This file has been built piece by piece by piece by piece. [If] somebody out there is thinking that there is one piece that is the smoking gun, one piece of information that has led to a break in the case, I'm here to tell you that this has been the compilation of an immense investigation."

Chief Hanson would not discuss why police believe the three family members are dead, saying only that the evidence "removed all doubt that it was a missing persons file [and] supported our now-firmly-held belief that it is a homicide." He would not discuss when police believe Nathan and Mr. Liknes, 66, and Ms. Liknes, 53, died. He did not reveal a motive.

Mr. Garland knew the family. There was no sign of forced entry at the Liknes home, where the three were last seen by Nathan's mother on June 29.

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Ian Savage, president of the Calgary-based Alberta Criminal Defence Lawyers Association, said it is rare for murder charges to be laid if no bodies have been found. He estimates it happens in only 1 per cent of murder cases.

"What this suggests is that the police have strong circumstantial evidence or forensic evidence or both," Mr. Savage said. "On the flip side [with no bodies], it means the chance of a successful defence improves."

Ed Ratushny, a law professor at the University of Ottawa, is a celebrated lawyer whose work in the field of criminal evidence has been published and cited by the Supreme Court of Canada.

"A case like [this] will turn on 'circumstantial' rather than 'direct' evidence," Prof. Ratushny said in an e-mail. "But in each situation, every essential element of the offence must be proven beyond a reasonable doubt. Obviously, there is no direct evidence such as a witness to the murder, so a jury would have to be satisfied beyond a reasonable doubt from the 'circumstances' that there actually was a murder as well as that the accused committed this murder."

Mr. Garland is scheduled to appear in court Aug. 6 on charges relating to identity theft. Police laid those charges early last week after they released Mr. Garland from questioning regarding the disappearances. The identity-theft charges meant he spent last week in the Calgary Remand Centre until he made bail Friday, which came with a string of conditions, including abiding by a curfew between 9 p.m. and 7 a.m.

Patti Garland, Mr. Garland's sister, is in a common-law relationship with Allen Liknes, one of Alvin and Kathryn Liknes's sons. Allen Liknes joined Rod O'Brien, Nathan's father, when Mr. Garland appeared in court July 4 via closed-circuit television on the identity-theft charges.

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Prime Minister Stephen Harper, Alberta Premier Dave Hancock and Calgary Mayor Naheed Nenshi all expressed condolences Monday. Nathan's parents work at Cenovus Energy Inc., and its chief executive also offered his sympathies.

Police lay first-degree murder charges when they believe they can demonstrate "preintent," Chief Hanson said. They apply second-degree murder charges when "preintent – the intent to commit the act – may not be there."

Nathan, who was just learning to print and has one older brother and one younger brother, was sleeping over at the Liknes home the evening of June 29.

"Nathan wasn't supposed to be there," Mr. O'Brien said in a press conference July 2.

With files from Kelly Cryderman