It's unclear whether the notebook was hand-made or a merchandised version designed for cosplay. But it had Death Note written on the cover along with at least one rule - those names written inside will die.
Within the pages, the adolescent had penned the names of over a dozen fellow pupils at Anthem Elementary School.
His family had already been concerned about the boy's depression. He'd been kept off school for the first part of the week - in early February 2014 - in order that he might calm down somewhat.
Once back in class, his teachers were tipped off when he sent a text to another student threatening suicide. The Death Note was discovered when his school-bag was searched, and local police department was duly alerted.
Parents of pupils at Anthem Elementary School received a robocall notice that a threat had been detected on the premises. Those whose names were on the list were personally called by the head teacher.
The boy never gave any indication that he planned to physically harm the other children. He seemed to hope that his Death Note would actually work.
He's now undergoing (presumably psychiatric) treatment, after which the school will decide what - if any - action they will take.