The transport ministry called on train operators Monday to step up security measures after a man went on a deadly random attack with a cleaver on a crowded shinkansen bullet train, reviving debate on how to balance passenger convenience with safety.

Police and train operators have become more vigilant against people trying to bring hazardous items on to trains following a self-immolation on a bullet train that killed an unrelated passenger in 2015. But in the latest case, the 22-year-old suspect simply carried the cleaver in his backpack.

Checking baggage in the same way as at airports, such as by using metal detectors, is widely viewed as impractical due to the huge numbers of passengers using bullet trains.

According to Central Japan Railway Co., which operates the line on which Saturday's crime took place, an average of 446,000 passengers used the Tokaido Shinkansen every day in fiscal 2015. The figure compares with around 170,000 domestic passengers each day at Tokyo's Haneda airport, the busiest in Japan.

The attack occurred about 10 p.m. on Saturday in the No. 12 car of the 16-car bullet train bound for Shin-Osaka Station from Tokyo. Soon after leaving Shin-Yokohama Station and an hour or so before the next stop in Nagoya, the suspect Ichiro Kojima took out the cleaver.

Knife rampage aboard Japanese bullet train kills 1, injures 2

(Photo supplied by passenger aboard the Nozomi 265)

According to JR Central, around 880 passengers were aboard the Nozomi 265, the day's last train bound for Shin-Osaka.

Passengers screamed out for help as Kojima wielded what some thought was an "axe." Kojima is believed to have assaulted two women before repeatedly slashing 38-year-old Kotaro Umeda in the chest and shoulders when he tried to protect them. Umeda died later in a hospital.

The incident exposed the limit of the safety measures JR Central has been working on -- such as the installation of security cameras in train cars and increased patrolling -- since a 71-year-old man set himself on fire on a Tokaido Shinkansen train in June 2015 with gasoline, killing himself and another passenger.

"A person with a strong intention of murder can do anything. Whether it is inside a shinkansen or on a street, the situation is the same," an official of JR Central said, indicating the difficulty of coming up with measures to prevent the same kind of incident from happening again.

The latest case also poses security challenge to Japan, with Tokyo scheduled to host the 2020 Olympics and Paralympics.

A 40-year-old man heading to Kobe from Tokyo on Monday said, "We need baggage checks as similar incidents could possibly occur in the future."
(Signboard at Odawara Station notifies passengers of train delays due to the incident)

A 32-year-old man, who always uses the bullet train for business trips, said, "Unlike airplanes, there are many users of shinkansen. I don't think it is possible to install even metal detectors."

"It is time for not only JR but also passengers to think about whether it is better to maintain bullet train convenience, like a commuter train, or to tighten security," Jun Umehara, a railway journalist, said, referring to railway operators.

Kojima, who was arrested after police stormed the train, was referred to prosecutors on Monday morning on a murder charge. He reportedly told investigators he slashed the three randomly with the cleaver because he was "feeling frustrated."

The two women, aged 26 and 27, were also taken to hospital with injuries to their head and shoulders, the police said.

Kojima has told the police that he had spent the last few months sleeping outdoors in Nagano Prefecture in central Japan. "I bought a cleaver and a fruit knife just before the incident," the suspect was quoted as saying.

His family said his whereabouts had been unknown since he left his grandmother's home in Aichi Prefecture, also in central Japan, about six months before. He was not on good terms with his parents and was adopted by his grandmother more than a year before.

He is also known to have told his family, "I am different from others. My life is not worth living."

On the day he carried out the attack, Kojima went to Tokyo Station from Nagano Prefecture by train and got on the shinkansen, the police said, quoting the suspect.

"I never thought that he would commit such a crime," Kojima's mother said in a statement, while also expressing her deep sorrow.

"I now regret that I did not take him back (home) even if he did not want to," the mother said.

Meanwhile, Umeda's family issued a statement through a lawyer, saying, "We do not have words to express the sorrow of suddenly losing a loved one."

Umeda's employer Hiroki Ishida, president of BASF Japan Ltd., also issued a statement and expressed his deep disgust at the perpetrator. "We heard he tried to help the women. We are proud of his bravery," he said.