The teenage boy had developed a concrete plan for when and how he would attack a specific preschool, Aftenposten and NRK report.
According to an arrest warrant, the boy is suspected of having planned to "attack several people in and at a named preschool" with a knife and several axes. These weapons and some form of manifesto were found during a search of his home in Vestfold county, on the western side of the Oslofjord.
The suspect has reportedly been in custody since mid-June, but the judiciary has prevented Norwegian media from reporting on the sensitive case until now.
The boy comes from an area outside Oslo and is being held in custody on the grounds that there is a real risk that he will kill or injure someone if he is released.
The threatening image was discovered when the boy had written posts online in which he threatened to stab women and girls. In police interrogations, he said that the plan was to take his own life and the lives of others.
The crime is an attempted act of terrorism, as the intention is believed to have been to instill serious fear in the population. A conviction could result in up to 21 years in prison.
