Sunday’s stabbing rampage on a Tokyo train by a man dressed up as the Joker from the "Batman" franchise was a sobering reminder of how vulnerable trains and subways are to violent, indiscriminate attacks in a metropolis heavily reliant on public transportation.

The incident, in which the assailant brandished what appeared to be a kitchen knife and set fire to cars on a Keio Line train on Halloween night, left 17 passengers injured. One of them, a man in his 70s, was in critical condition after reportedly being stabbed in the chest. After assaulting the man, the assailant, identified as 24-year-old Kyota Hattori, went on to scatter flammable fluid and burn a seat, causing the train to fill with smoke.

Hattori was arrested at the scene for attempted murder. He later told investigators that his motive was to “sentence himself to death” by killing two or more people.