A video has been shared on Twitter showing the suspected attacker sitting calmly on the train and smoking as he waits for police to detain him.
Dressed in a Joker costume from the Batman franchise, the 24-year-old man is suspected of injuring at least 17 people on Sunday during a knife, arson and, acid attack.
According to the NHK TV channel, the attacker told the police that he wanted to kill in order to be sentenced to death.