A forensic pathologist giving evidence at an inquest into the death a father and his two sons say the cause of the children's death was "un-ascertained."
Amanda Jeffrey told the court both boys had the sleeping drug Zopiclone in their blood stream.
11 year old Jack had a relatively small amount but 3 year old Bryn had a higher dose that may have killed him. She said Jack may have been smothered.
Their father, Graham Anderson, was found with a neck injury and a belt around his neck.