Calgary police say two charges of first-degree murder and one charge of second-degree murder are pending in the disappearance of five-year-old Nathan O’Brien and his grandparents, Alvin and Kathy Liknes.

Chief Rick Hanson says a man has been arrested but he can't identify him because the charges have not been officially laid.

Hanson says bodies have not been found, but an Amber Alert issued shortly after the group was reported missing has been cancelled.

"Evidence has led us to believe they are dead," Hanson told reporters.

However, he said that there is no single piece of evidence – no "smoking gun" – that led to the arrest of the suspect. Instead, investigators have been working for the past two weeks on a "putting a very complex case before the courts."

Earlier Monday, Douglas Garland, a man who police had previously questioned in the case of a missing Calgary family, was taken back into police custody.

It is unclear whether he is facing new charges or why he was arrested.

Hanson offered his condolences on behalf of police to the Liknes and O'Brien families Monday.

"There's always a glimmer of hope and unfortunately with the laying of the charges we've taken that away from the family," said Hanson. "They're devastated."

Calgary Mayor Naheed Nenshi also tweeted his condolences.

Nenshi continued his remarks in an emotional statement:

"I, like all Calgarians, am terribly saddened to learn about the murder charges that were laid today related to the missing persons investigation in our community. My heart goes out to the Liknes and O’Brien families, and I know that they will continue to have the support they need from all of us at this very difficult time. My thanks go to my colleagues at the Calgary Police Service and the women and men of the RCMP for their hard work on this investigation."

Prime Minister Stephen Harper also offered his support to the families:

The family haven't been seen since June 29 after what police say was a violent incident in the Liknes home.

Nathan was at his grandparents' for a sleepover and when his mother arrived to pick him up the next morning everyone was gone

Garland is the only person of interest identified in the case. Police spent more than a week searching his parent's acreage in Airdrie, where he has been living.

Police are still asking people near the Airdrie farm to check their properties and to call them if they note anything out of the ordinary.

Garland has ties to the Liknes family. His sister is in a relationship with a member of the Liknes family and he had business dealings with Alvin Liknes as well.

Garland had been questioned on the disappearance and arrested on an unrelated charge involving identity theft.

Garland was released on bail last Friday.

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  • Mourners have placed flowers, notes and teddy bears at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014.

  • Flowers and teddy bears are shown at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014. A man who has been under investigation in the disappearance of a Calgary boy and his grandparents has been formally charged with their murders.

  • Bobbi-Jo Zimmer, from High River, Alta., and her children, left to right, Tayvon, two, Braylon, seven, and Dawson, nine, place flowers at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014.

  • Mourners have placed flowers, notes and teddy bears at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014.

  • Kelley MacAuley observes a memorial after placing flowers at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014.

  • Jennifer Kohut, centre, embraces her sons Axton, left, three, and Cadon, five, after placing flowers and toys at an impromptu memorial for Nathan O'Brien and his grandparents, Alvin and Kathryn Liknes, at the Liknes home in Calgary, Alta., Tuesday, July 15, 2014.

  • Douglas Garland is escorted into a Calgary police station in connection with the disappearance of Nathan O'Brien and his grandparents in Calgary, Alta., Monday, July 14, 2014.

  • Douglas Garland is escorted into a Calgary police station in connection with the disappearance of Nathan O'Brien and his grandparents in Calgary, Alta., Monday, July 14, 2014.

  • Douglas Garland is escorted into a Calgary police station in connection with the disappearance of Nathan O'Brien and his grandparents in Calgary, Alta., Monday, July 14, 2014.

  • Douglas Garland is escorted into a Calgary police station in connection with the disappearance of Nathan O'Brien and his grandparents in Calgary, Alta., Monday, July 14, 2014.

  • Calgary Police Chief Rick Hanson says first and second degree murder charges are being filed in connection with the disappearance of Nathan O'Brien and his grandparents at a news conference in Calgary, Alta., Monday, July 14, 2014.

  • Calgary Police Chief Rick Hanson says first and second degree murder charges are being filed in connection with the disappearance of Nathan O'Brien and his grandparents at a news conference in Calgary, Alta., Monday, July 14, 2014.

  • Calgary Police Chief Rick Hanson says first and second degree murder charges are being filed in connection with the disappearance of Nathan O'Brien and his grandparents at a news conference in Calgary, Alta., Monday, July 14, 2014.

  • People comfort each other at a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • People comfort each other at a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Volunteers prepare candles at a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • A photo collage of the Liknes and O'Brien family is displayed as neighbors, friends and relatives hold a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Rod O'Brien, centre, tears up as he looks at a photo collage of the Liknes and O'Brien family during a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • A photo collage of the Liknes and O'Brien family is displayed as neighbors, friends and relatives hold a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Rod O'Brien, centre, father of Nathan O'Brien, attends with neighbors, friends and relatives, a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Jennifer O'Brien, left, mother of Nathan O'Brien, attends with neighbors, friends and relatives, a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Rod O'Brien, and Jennifer O'Brien attend a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Neighbors, friends and relatives hold a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Rod O'Brien, right, and Jennifer O'Brien, centre, attend a candlelight vigil for missing Calgarians Nathan O'Brien, five, and his grandparents Alvin and Kathryn Liknes in Calgary, Alta., Thursday, July 10, 2014.

  • Police investigators comb a hay field north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators use an inflatable raft in a slough north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators prepare to search a hay field north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators prepare to search a hay field north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators prepare to search a hay field north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators prepare to search a hay field north of Airdrie, Alta., Monday, July 7, 2014, looking for clues to the disappearance of three people.

  • Police investigators at a rural residence north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators comb a hay field north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators comb a hay field north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators comb a hay field north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators comb a hay field north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators comb a hay field north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators at a rural residence north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Police investigators at a rural residence north of Airdrie, Alta., Saturday, July 5, 2014, looking for clues to the disappearance of three people.

  • Rod O'Brien wipes his tears while holding a butterfly made by his son as he speaks to the media about his son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Rod and Jennifer O'Brien show their emotions as they speak to the media about their son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Rod and Jennifer O'Brien left, look on as Jeff Liknes, second from right, speaks to the media about his nephew Nathan O'Brien and his parents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Jennifer O'Brien holds a piece of her son's clothing while speaking to the media about her son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Jennifer O'Brien holds a piece of her son's clothing while speaking to the media about her son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Rod O'Brien wipes his tears while holding a butterfly made by his son as he speaks to the media about his son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Rod and Jennifer O'Brien show their emotions as they speak to the media about their son Nathan O'Brien and his grandparents Alvin and Kathryn Liknes during a press conference in Calgary on Wednesday, July 2, 2014.

  • Nathan O'Brien is described as three feet tall, curly blonde hair, brown eyes, and was last seen wearing peach-coloured shorts and a blue-striped hoodie.

  • Kathryn Liknes is five-foot-three-inches tall, 120 pounds with reddish-brown hair and green eyes.

  • Alvin Liknes is six feet tall, 200 pounds with grey and blond hair and was wearing black shorts. Alvin has a distinctive walk.

  • Calgary police investigators check out the home where five-year-old Nathan O'Brien and his grandparents Alvin and Kathryn Liknes disappeared, in Calgary, Alta., Wednesday, July 2, 2014.

  • Nathan O'Brien and his grandmother Kathy Liknes are shown in a Calgary Police Service handout photo. Calgary's police chief questions whether a reward would help the investigation into the disappearance of a five-year-old boy and his grandparents.

  • Police tape cordons off the home where five-year-old Nathan O'Brien and his grandparents Alvin and Kathryn Liknes disappeared, in Calgary, Alta., Wednesday, July 2, 2014.