The 16-year-old from Linz saved the online conversation and took it to Austrian police who contacted German colleagues, Lower Austria’s police department said in a statement.
A search at the suspect’s home in the town of Uslar revealed several knives, a bow, a list of names and a farewell note. The teenager said he had been harassed at school. He is undergoing a mental health check.
Austrian Interior Minister Wolfgang Sobotka said, in a comment cited by the national ORF radio, the incident showed how important cross-border cooperation was for police operations.