Police found his devices contained images from conflicts in Gaza, Ukraine, Sudan and Korea, as well as copious academic material relating to war and genocide.
His search history revealed an interest in Nazi Germany, ethnic violence in Somalia and Rwanda, and slavery.
Detectives also found an American academic study of an al-Qaeda training document, which had been downloaded at least twice since 2021.
A picture of the teenage killer's descent into violence has emerged since he carried out the murders.
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