A teenager shot and killed three children and a teacher on Thursday at an elementary school in the US state of Oregon, police said, adding the assailant was later killed by an armed bystander who pursued him into the building. Officers rushed to Silver Rail Elementary in Bend, a city of about 100,000 in the nation’s northwest, after reports of a shooter on campus on Thursday afternoon. The three children who died on the scene were aged five, eight and 11, said Bend police chief Mike Krantz.