The teenager identified as Ali Sonboly, who shot dead nine people and injured 27 others in Munich, had no links to the Islamic State, but he had amassed literature relating to killing sprees and police responses to them.
Officials said the searches had revealed no links to Islamic State, and suggested the attack was unlikely to have been motivated by Islamist extremism.
However, they found newspaper clippings and books related to killing sprees, one of which was believed to be a textbook called Why Kids Kill: Inside the Minds of School Shooters.
The German Police said the gunman, who opened fire at a crowded shopping centre and McDonald’s restaurant on Friday evening, was an 18-year-old German-Iranian, who had been raised in Munich and had no prior criminal record, reports the Guardian.
The officials added there were indicators that the shooter had been in psychiatric care and was treated for depression. Sonboly, was a “shy, lazy” teenager who used to shirk his job as newspaper delivery man, according to his neighbours.