07/03/2014 01:29 EDT | Updated 09/02/2014 05:59 EDT

Nathan O'Brien Missing: Calgary Police Interview Witnesses

CALGARY - Calgary police say closed-circuit video and tips from the public are bringing them closer to understanding what happened to a missing five-year-old boy and his grandparents.

But homicide unit Staff-Sgt. Doug Andrus said investigators still don't have any suspects they can name.

"We have no suspects we can name, but ... we have information that's allowed us to move forward with this investigation," Andrus said at a news conference Thursday.

"I think everyone here, first of all, wants to ensure that we do a complete and thorough investigation. We identify the people responsible and we hold them accountable and I don't want to do anything to jeopardize that.

"Are we closer than yesterday, I would say we are."

Nathan O'Brien and Alvin and Kathy Liknes were reported missing Monday and police believe their disappearance is suspicious.

The boy had been at his grandparents' on a sleepover after the couple held an estate sale at their home on the weekend. Police have said there was evidence the three may have been forced from the home.

An Amber Alert remained in effect.

Andrus repeated what he said Wednesday when Nathan's parents made an impassioned plea for the return of their son.

"We're very confident that we are going to find these family members and we are hoping that we are going to find them alive," he said.

Andrus said officers have closed-circuit video from homes and business near the Liknes' house and it's helping with the investigation.

He said police are also getting information from the public, including the people who attended the estate sale.

Police had asked anyone who attended the sale and bought something to bring a photo of the item to a community centre Thursday and speak with investigators. Six tables manned by police officers with notepads were set up inside for interviews.

Andrus estimated as many as 300 people attended the sale. He said between 20 and 30 had gone to the community centre as of Thursday afternoon.

"I would say it is less a mystery to us. I can't comment on the degree. Again, we are getting good information coming in and we are going through it and determining the relevance to the investigation," he said.

Police also took family members through the home to get a better sense of whether anything was missing.

The grandparents were planning a move to Edmonton and then on to Mexico when they disappeared.

Police have said there are no custody issues with the family — the boy's parents are married and he is their biological son. Police have also said officers have no history with the family. All of the family's vehicles have been accounted for.

A blog has been established so Canadians can send messages to the family along with information on how to reach Crime Stoppers.

One person wrote about meeting the missing boy once at a birthday party.

"Nathan was such a graceful and polite little man," said the poster who gave the name Susan Bergquist.

"We are doing all we can here in Red Deer to help out with social media and will be here for any further efforts to help with the return of Alvin, Kathy and Nathan."

Another person offered a message of hope.

"Every day, I am thinking of Nathan and his grandparents. I believe that they will come home safe to their family," wrote the person who gave the name Selina Bishop.

"The police are working hard to solve this one. Someone saw something, and today they will find that someone — and that will be the clue that leads them to Nathan. Stay strong. Love each other."

— Follow @BillGraveland on Twitter

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