CALGARY - Calgary police say a man taken in for questioning in the case of a missing five-year-old boy and his grandparents is not the only lead in their investigation.

But spokesman Kevin Brookwell isn't willing to discuss what other angles police are pursuing.

"There are other investigative leads we are following up on, so he is not the only person of interest that we are looking at," Brookwell told reporters Tuesday.

Asked to clarify, Brookwell backed away from suggesting there were other persons of interest in the case.

"He's ... a person of interest that we have interviewed, but there are other investigative leads that we are following up on."

Douglas Garland was taken into custody over the weekend for questioning in the disappearance of Nathan O'Brien and his grandparents, Alvin and Kathy Liknes, who have been missing since June 29.

Court records show Garland, 54, has a criminal past involving drugs and identity theft and Calgary police confirm his sister is in a relationship with a member of the Liknes family. Garland remains in custody on an unrelated charge.

An Amber Alert remains in effect and police are still searching the rural property and surrounding area where Garland lives north of Calgary.

Brookwell said sightings of the three missing people have been reported across the country and police still hope they will be found alive.

He said several items have been seized from the property and sent to the crime lab for testing, along with a green pickup truck matching one seen on closed-circuit video in the Liknes's neighbourhood the night they disappeared.

Nathan had been at his grandparents' on a sleepover the night of June 29 after the couple held a sale at their Calgary home on the weekend. They were selling their things as they prepared for a move to Edmonton and then on to Mexico.

When his mother went to pick Nathan up the next morning, no one was home. Police have said there was evidence of a violent incident in the house. They have not disclosed a motive.

Yellow police tape remained in place at the home in Calgary's Parkhill neighbourhood Tuesday afternoon. A lone police officer sat in his car out front. Residents of the neighbourhood just south of downtown are planning a candlelight vigil for Thursday evening.

Officers have spent a lot of time trolling a large pond and grassy fields near the Garland property north of the city.

Story continues after the slideshow

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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.

Court records say Garland served time in prison for making amphetamines at his parents' farm.

A federal tax court ruling from 2005 shows Garland went to medical school for a year but left after having a mental breakdown.

The document says after Mounties raided his parents' property in 1992, he was released on bail and fled to Vancouver, where it says he assumed the name of a dead person named Matthew Kemper Hartley. A cemetery website lists a 14-year-old boy with the same name who was buried in southern Alberta in 1980.

Justice officials say Garland pleaded guilty to two counts of drug trafficking and was sentenced to 39 months. He received an additional one month for possession of stolen property.