Calgary police say they are pursuing “other investigative leads” in the case of a missing five-year-old boy and his grandparents, after a “person of interest” was questioned over the weekend.

Police spokesperson Kevin Brookwell didn’t divulge details, but he told reporters Tuesday that investigators are optimistic that Nathan O’Brien and his grandparents, Kathy and Alvin Liknes, will be found alive.

The man identified as a “person of interest” in the case, Douglas Garland, was questioned over the weekend. He has not been charged in connection with the disappearances, but he was arrested on an unrelated identity theft charge.

After Brookwell suggested Tuesday that Garland was not the only person of interest in the investigation, he clarified that police are following up on “other investigative leads.”

Police did confirm that Garland has a connection to the Liknes couple – his sister is in a relationship with a member of the Liknes family.

Garland has a history of living under an assumed name and he spent time in jail for making amphetamines at his parents’ farm, according to court records.

Nathan and his grandparents have been missing since June 29. The Liknes had just wrapped up an estate sale at their home and Nathan stayed with them for a sleepover. When his mother went to pick him up the next day, all three family members were gone.

Police continue to search the property near Airdrie, Alta., where Garland lived with his parents, as well as the surrounding area.

Brookwell said a green pickup truck seen in the Liknes’ neighbourhood was seized from the property, but it’s not yet clear whether the vehicle is relevant to the investigation.

Several items have also been seized and sent to the crime lab for analysis, he said.

“The search will continue until no stone has been left unturned,” Brookwell said.

Police are still appealing to the public for help and are asking anyone who may have information about the case to contact them.

Investigators have been asking those who attended the estate sale at the Liknes’ home to come forward and bring photos of the items they bought. Of the estimated 200 people who were at the sale, 88 have come forward so far, Brookwell said.