Among the evidence found in the apartment were a total of 16 starter pistols, air rifles, and paintball guns, in addition to chemicals meant for building bombs, police said.
Armed with a starter pistol and a knife, the young man entered the school where he stabbed his 58-year-old former mathematics teacher. Autopsy results on Friday revealed that the man died of multiple stab wounds to the heart.
After his arrest at the crime scene on Thursday the suspect admitted to killing the teacher because he was angry about being given poor marks, police said.
Police have also discovered both written and electronic evidence that points to long-term planning of the attack, including the use of an internet forum called “school shooting.”
It has also become clear that the 10 am fire alarm that alerted the first police officers to the scene was activated by the suspect himself so he could attempt to disappear into the crowd, chief public prosecutor Lothar Liebig said.
“I assume it was planned and targeted approach,” Liebig said, adding that there appeared to be no evidence the 23-year-old planned to commit further violence at that point.
Liebig said the young man, who has unsuccessfully looked for an apprenticeship since he finished school in 2004, may have acted out of frustration.
On Friday scores of students at the school in the city’s Mundenheim district laid flowers at the crime scene in memory of their teacher. Some also took advantage of counselling services provided to help them deal with their grief and shock.
German authorities have been especially alert to violence at the country's schools since a 17-year-old boy when on a rampage that left 15 people dead in the town of Winnenden last March.