Two 14-year-old boys were arrested on charges of threatening a "large-scale shooting" at a high school, a threat investigators considered credible.
Investigators arrested the boys Monday at Clear Lake Middle School, where they are students, sheriff's Sgt. Candi Baker said. The threat was aimed at Ranum High School, Baker said.
She declined to say why or what the motive might have been.
The boys were being held in a juvenile detention facility.
Last Friday was the eighth anniversary of the Columbine High School massacre just south of Denver in Littleton. Ranum High School is in the suburbs north of Denver.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969