The 37-year-old defendant Tsushima Yusuke is charged with the attempted murder of three passengers on the Odakyu railway in August 2021.
He is accused of stabbing the chest and back of a woman who was a university student at the time, and two others. The woman suffered serious injuries that took about three months to heal.
At his first hearing at the Tokyo District Court, the defendant admitted to the charges.
His lawyer argued that the degree of murderous intent was not strong enough to kill any passengers, and that the defendant only thought that he "didn't care if they died or not."
The prosecutors said the defendant felt that his friends and other women looked down on him, and that he had a feeling he couldn't forgive them or wanted to die.
They explained that this led him to want to kill "successful" people. They said he wanted to do this by spraying kerosene on a train full of defenseless people.
Stabbing on a Tokyo commuter train
The incident took place on an Odakyu Line commuter train at around 8:30 p.m. on August 6, 2021.
The defendant allegedly wielded a knife on a rapid train operating near Seijogakuen-mae Station in Tokyo's Setagaya Ward. The incident left 10 passengers injured.
Investigative sources said the man got off the train after it made an emergency stop and ran away.
They said the knife believed to be the weapon used in the crime as well as a mobile phone believed to belong to the man were found inside the train car.
Tsushima was located at a convenience store around 5 kilometers away from the scene about 90 minutes after the incident.
Police arrested him on suspicion of attempted murder. They said he told investigators during questioning that he had targeted a rapid train which stopped at fewer stations to prevent passengers from escaping.
Security camera footage shows the suspect slashing passengers and trying to ignite a fire by spraying cooking oil inside the train.
Victim 'still remembers the scene'
A man in his 40s who lives in Kanagawa Prefecture was in the train car next to the one where the incident occurred. He fell on top of other passengers as he fled, injuring his lower back and other parts of his body.
He described the scene in an interview with NHK a week later, saying he feared he might be killed as he failed to escape.
The man spoke with NHK again recently and said that he still remembers the incident.
He said that seeing graphic videos or social media posts reminds him of what happened to him that night. He said that he sometimes remembers being chased by the criminal, the feeling of the train's floor after he fell, and his fear of failing to escape.
While he uses trains to commute to work and other places, he said he learned that a train car is a closed room from which escape is not always possible. He said that he has started to check what kind of people are around him whenever he boards a train, as well as the locations of emergency buttons and security cameras.
The man said that he is very angry about the "senseless" incident that injured people with no relation to the suspect. He said that he cannot understand why the suspect would take such actions, which would obviously hurt not only the victims but also his own family and friends.
Japan shaken by series of train attacks
Two months after the August attack, a similar incident took place on a different commuter route in Tokyo. A man was indicted for a knife and arson attack on a Keio Line train in October 2021.
His trial opened on Monday. Prosecutors argued that the defendant saw reports about the Odakyu Line case, which inspired his desire to "burn and kill many passengers."
The series of indiscriminate train attacks prompted the government and railway companies to step up efforts to protect passengers' safety.
The Ministry of Transport's measures include recommending upgrades such as security cameras to monitor the situation inside trains. It also established guidelines to urge operators to improve their displays about the functions and use of emergency equipment.
A government panel recently approved a plan to require train operators to install security cameras on newly manufactured cars for high-density routes, as well as on all Shinkansen bullet trains, as early as September this year. Most Shinkansen operators have already met the requirement.
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Tokyo passengers wary, prone to panic
An incident on a Tokyo train this week reminded passengers of the past attacks, and led some to panic.
A passenger pushed an emergency button in a JR Yamanote Line train approaching Shinjuku Station on Sunday after a man was seen carrying a knife. Three people were injured in the rush to flee the train.
The man told police that he is a cook and he was on his way home from work. He said he had covered his knife with a towel but it slipped off when he fell asleep.
Expert: Passengers' awareness is important
A security expert said cameras are helpful in understanding what is happening in the cars, but the devices are not a "silver bullet" for safety.
Itabashi Isao, chief analyst at Japan's Council for Public Policy, said security camera footage can help police and railway officers promptly handle a situation. But he also said cameras themselves do not deter incidents.
He emphasized that passengers should have a mindset that the inside of a train is not always safe, and need to be cautious about what is happening around them.