Calgary police investigating the disappearance of a five-year-old boy and his grandparents say there was a violent incident in the home where they were last seen.

Staff-Sgt. Doug Andrus says police found forensic evidence at the home, but didn’t say what it was.

He says police believe it was from someone in medical distress.

The evidence has been sent to a police lab for analysis.

Five-year-old Nathan O’Brien and his grandparents — Alvin and Kathy Liknes — were reported missing Monday morning by the boy’s mother.

Police are looking for the driver of a green Ford F-150 pickup that was noticed several times in the area on Sunday night when the three were last seen.