Rigby Police Chief Keith Hammon says the boy's parents called police Monday when they found the list on an electronic tablet.
The Post Register reports officers found a bag of weapons at the boy's home, including multiple knives, handguns and ammunitions.
Hammon says bullying at the boy's school, Rigby Junior High, was a factor. The parents of the students on the list have been notified, and the police officers on the list were not identified.
Hammon didn't say how many people were targeted or how many weapons were in the bag.
Police planned to transport the boy to the Behavioral Health Center in Idaho Falls for a mental health evaluation.
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