A 24-year-old man wearing a Joker costume attacked passengers on a Tokyo train line on Sunday evening.
As many as 17 people were injured as they headed for Halloween parties in the city.
Witnesses say the suspect was wearing a green shirt and purple suit.
He sprayed a clear liquid around the carriage and set it alight. Video footage showed passengers running through carriages away from the flames while others clambered through windows.
“I thought it was a Halloween stunt,” one witness told the Yomiuri newspaper about the attack. “Then, I saw a man walking this way, slowly waving a long knife.”
The attack happened at around 20:00 local time (11:00 GMT) near Kokuryo station, in the city’s western suburbs.
Media reports say the man was arrested by police on the spot.
According to news outlet Kyodo, he told police he adored the character Joker in the Batman comics.
The Joker is a super villain in the comics and batman’s archenemy. The 2019 hit movie Joker, starring actor Joaquin Phoenix, featured a scene where he attacks several men on a train after being repeatedly harassed by them. It’s a pivotal moment, marking the beginning of the character’s transformation into the Joker.
The NHK news agency quoted police as saying that the man had said he had “wanted to kill someone since June” because he had quit his job and seen many of his friendships fall apart.
It added that he dressed like the Joker because he “looked up to him”.
Local media reports say that the suspect told authorities he wanted to kill people so he could be sentenced to death.
The AP news agency, citing the Tokyo Fire Department, said three of the injured had serious wounds. Local media reports an elderly man was unconscious after being stabbed in the attack.
Video from the scene shows passengers running from the attacker, stumbling through a connecting door between carriages and climbing through the train’s windows after it made an emergency stop.
Shunsuke Kimura, who filmed one of the videos, told the national NHK broadcaster that the scene was “horrifying”. “Train doors were closed and we had no idea what was happening, and we jumped from the windows,” he said.
Violent crime is rare in Japan but there have been a number of high-profile knife attacks in recent years.
Ten people were injured by a knife-wielding man on another Tokyo commuter train in August. In 2019, a man attacked a group of schoolchildren waiting for a bus in Kawasaki, killing two and injuring at least 18 others.