A violent crime happened at the last place a missing five-year-old boy and his grandparents were seen, Calgary police said Friday. 

Nathan O'Brien and his grandparents, Kathy and Alvin Liknes, have not been seen since Nathan's mom left the Liknes' home Sunday night. When she returned to pick Nathan up Monday morning, all three were gone — and there were signs that they had not left willingly, say police.

"We can now confirm that a violent crime happened in that residence," said Calgary police Staff Sgt. Doug Andrus.

"Forensics experts continue to analyze evidence found at the scene in order to determine the exact nature and extent of crime, as well as who the potential victims are."

Andrus added the case is still a missing person investigation and the Amber Alert remains in effect. 

“We remain hopeful that we will find them alive," said Andrus, who is with the Calgary Police Service's homicide unit.

“But based on the evidence, I would say someone would be in medical distress."

Andrus said they are not able to say how many people may be in medical distress, but said they have "sent the exhibits away," and are awaiting results. 

Search for Ford F-150 truck, driver

Police Nathan car

Police are looking to speak with the driver of this Ford truck in connection with the disappearance of three Calgary family members. (Calgary Police Service)

Based on CCTV video, police are looking for a Ford F-150 truck that was seen driving around the area several times in the course of the night. Police want to speak with anyone who was in that vehicle, or who may have more information about it. 

“We just believe given the area the vehicle was in, and the fact that it was the night of the incident and that it drove in the area several times, that there's a good possibility that the individual, or individuals, may have information," said Andrus.

The truck is described as:

  • A late 1980s or early '90s Ford F-150.
  • Green.
  • Appears to have been kept in very good condition.

For the past week, investigators have been interviewing neighbours and are looking to speak with everyone who attended the estate sale Friday, Saturday or Sunday. The O'Brien family had been over helping out with an estate sale.

Police say they are pleased with the progress being made so far in the investigation. 

"I would say it's less a mystery to us," said Andrus. "Are we closer than yesterday? I would say we are."

Police hoping for the best

On Thursday, police said they still don't know the motive behind their disappearance and "have no suspects [they] can name."

Investigators say they are working with the Canada Border Services Agency and partner agencies in the U.S.

Police say they have had a tremendous response from the public, including tips, and are working hard to keep moving the investigation forward.

The chief of the Calgary Police Service said he is convinced someone knows something about the disappearance.

Search for information continues

A website has been set up for people to offer messages of support to the family.

The site has been created as a dedicated place for those messages after police say support began rolling in from across Canada. 

It also contains information on how people can submit tips to Crime Stoppers.

Anyone with information or who attended the Liknes's estate sale is still being asked to come forward to speak with Calgary Police Service, which can be reached at 403-266-1234, or Crime Stoppers, which is at 1-800-222-8477.

Investigators say people may not even realize they know something that could help the investigation and so they are looking to talk with as many people as possible.

Community shocked 

Neighbours say they are dumbfounded by whole situation. 

Christie Simmons lives two doors down from the grandparents' home in Parkhill.

"These are my neighbours. These are normal, grounded, everyday people like us, you know, so I guess that's the whole thing. It ends up feeling like it's hitting a little close to home. You know, it makes you wonder about your own safety."

Simmons says everyone in the neighbourhood hopes Nathan and his grandparents will be found soon.

Elsewhere, three bodies were found Friday in a car near Barrie, Ont. Police released few details, but told CBC News the discovery is not connected.