CALGARY—Calgary police investigating the disappearance of a 5-year-old boy and his grandparents say there was a violent incident in the home where the three were last seen five days ago.

Homicide unit Staff-Sgt. Doug Andrus said police found forensic evidence at the grandparents’ home but wouldn’t say what it was.

“Based on what we saw at the scene we believe there was a violent incident inside the residence,” Andrus told a news conference Friday.

“We’ve sent the exhibits away and we will have a better understanding of that once we get the results back from those exhibits. But based on the evidence, I would say that somebody would be in medical distress.”

• Progress being made in missing Calgary boy case: Police

Nathan O’Brien and his grandparents Alvin and Kathy Liknes were reported missing Monday morning by the boy’s mother. The boy had been at his grandparents’ for a sleepover after the couple held an estate sale at their home on the weekend.

Nathan’s parents appeared in front of reporters and cameras earlier this week and made a tearful plea for the return of the three. Rod O’Brien urged his son to be a superhero and stay strong.

Police initially said evidence in the home suggested that its residents didn’t leave voluntarily and their vehicles were all accounted for.

Andrus added Friday there were no signs of forced entry at the house. He said police still don’t have a motive for what took place.

“I can’t go into details about what we found in the residence,” he said. “We are continuing to assess that information and we are still hopeful we will find these individuals alive.”

Police are looking for the driver of a pickup that was noticed several times in the area on Sunday night when the three were last seen.

A picture of the truck captured on closed-circuit video shows a late ’80s or early ’90s green Ford F-150 in very good condition. Police aren’t calling the driver of the truck a suspect but believe that person may have more information about the missing people.

Investigators put out a call to the more than 200 people they believe went to the estate sale at the Liknes’ home. The pair were selling their things in perpetration for a move to Edmonton and then on to Mexico.

Andrus said officers spoke to about 75 people on Thursday.

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