The young man, wearing an all-black outfit with explosives attached to his body, entered the Geschwister-Scholl school in Emsdetten near the Dutch border on Monday morning and randomly opened fire at students. He injured at least 32 people, two of them seriously, before he raced off for the school's second floor after he ignited smoke bombs.
Police that arrived roughly half an hour later on the scene found him dead on the floor with two sawed-off shot guns lying next to him, according to Deutsche Welle Online. Bomb experts were called in to remove the explosives from his body.
An autopsy revealed that he had committed suicide by shooting himself in the head, police said Tuesday.
Police union officials have called for a thorough investigation how the youth got his hands on the weapons and the explosives.
A frenetic player of the violent computer game "Counter Strike," the boy was a loner at his former school and wanted to retaliate for being mocked, he wrote in a Web forum.
"The only thing I really learned at school was that I'm a loser," the youth wrote in a letter posted on his Web site that was later removed by police. "I hate people ... I'm gone."
The shooting has caused German politicians to call for stricter regulations against violent computer games and the need for school psychologists, who would be able to help outsiders at school.