In the attack on a regional train between Kiel and Hamburg with two dead and seven injured, witnesses held the attacker.
According to the Itzehoe police, the witnesses managed to stop the suspect immediately after the crime, until the emergency services arrived at the train station in Brokstedt.
The man is said to have previously attacked several people with a stabbing weapon on the train.
Brokstedt - The background to the crime was initially unclear.
dpa