CALGARY - Investigators are returning to the scene of the crime in the disappearance of a five-year-old Calgary boy and his grandparents.

Police say they will sweep the property of Alvin and Kathy Liknes as part of a three-pronged attack today, searching for more clues.

The couple and their five-year-old grandson, Nathan O'Brien, disappeared from the home on June 29.

Police say there is evidence a violent crime occurred there.

Searchers also continue to comb the rural property of person-of-interest Douglas Garland near Airdrie, north of Calgary, as well as several surrounding acreages.

Police are also sifting through mounds of garbage at a northwest Calgary landfill.

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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.