15-year-old Girl Cut Off Her Classmate’s Head

Despite signs of her failing mental health, no one intervened.

In a small town in Nagasaki, Japan, a 15-year-old girl named Aiwa Matsuo decided to hang out with her classmate. They went shopping, got some food, and headed back to the girl’s apartment. The girl lived alone and Aiwa thought it would be fun to hang out at her place with no parents around to bother them. But the girl had other plans.

The girl beat, strangled, killed, and dismembered Aiwa, including cutting off her head. The murder shocked not only the town but the nation as it was rare to hear of crime, especially murder. And even more shocking was that both girls were 15 and not involved in any drugs, gangs, or other criminal activity.

Why did the girl kill Aiwa? Was it because of an argument or bullying? Did the girl lure Aiwa to her home planning to kill or was it a spur-of-the-moment decision? Was the girl’s mental state a factor in the murder? What happened to the girl? Find out about the tragic story of Aiwa and why the whole event could have been prevented.

The Crime

“I came home with her so I could kill her”

It was 2014 in Sasebo, Nagasaki, Japan. In the same city, 10 years prior, a 10-year-old girl slashed her friend’s throat in a classroom during lunchtime. The girl suffered from autism and the case put Sasebo City on the map.

Japan and the city of Sasebo were slowly trying to heal and forget about the vicious crime that rocked the town. However, on July 26, 2014, the town would once again become the center of attention.

A girl, whose identity has never been released because she is a minor attended the same high school as Aiwa Matsuo. Aiwa and the girl were classmates but were more acquaintances, rather than friends. But the girl invited Aiwa out on a Saturday to do some shopping and hang out. The girl told police, “I told her [Aiwa] that I wanted to see her and asked her to come.”

The girl whose mother died of cancer the year prior, and whose father remarried, was living in an apartment alone. The girl invited Aiwa to her apartment in order to kill and dismember Aiwa. She had tools, including hammers, knives, and a saw, that police discovered later.

Around 8 pm in her apartment, the girl struck Aiwa in the back of the head over 10 times with a blunt instrument, most likely a hammer. She then used a cord and strangled Aiwa to death. Aiwa was then placed on the girl’s bed where the girl began using her “tools” on Aiwa’s body.

She told police, “I wanted to kill some and dissect a dead body…I bought the tools by myself.” Aiwa’s body was found decapitated. The girl also severed Aiwa’s left hand and split her abdomen open. The apartment also had medical textbooks that the girl used for reference.

At around 10 pm, just a couple of hours after the girl murdered Aiwa, she started posting messages and pictures on 2Channel, a Japanese internet forum like Reddit and 4Chan. The images were of bloody clothes and bloody hands. Here are some of the messages she wrote:

“I have ended up killing.”

“Oh no, blood keeps pouring out even though I have wiped it away many times.”

“I’ve tried to warm [the body] as it got cold, but it doesn’t warm up … Everyone, [do you want to know] what color the brain is? … I’ll take good care of the brain and the spinal cord, putting them in a solution.”

The police arrived at the girl’s apartment the next day after the pictures were posted, on the suspicion of murder. When they entered the apartment they found Aiwa’s body on the girl’s bed and various tools she used to kill and dismember her around the apartment. The girl quickly confessed to police saying she had no animosity towards Aiwa but, “she wanted to try dissection techniques on a human being after reading medical textbooks and practicing on a cat.”

She also told police during interviews that she had a desire to kill someone since she was in elementary school.

The Victim

Aiwa Matsuo was a cheerful, kind, and positive girl who always had a smile on her face. A fellow member of the school photo club that Aiwa was part of said, “Aiwa was a nice and cheerful girl. I still can’t believe what happened.”

The funeral was attended by several hundred people, one of whom, who knew Aiwa said, “She was a cute one. I can’t take what happened. I just hope I can do something for her dejected parents,” reported the Japan Times.

Aiwa’s parents also released a statement saying, “We cannot bring ourselves to face the incident, as it struck us so suddenly. Aiwa was our treasure and we had raised her with love. We now only hope to calmly send her off.”

The Killer

The girl who took Aiwa’s life on July 26th gave many signs throughout her childhood that she was a danger to others and needed help. Reports revealed that she had a history of dissecting small animals as a child. After an investigation was done from friends, family, classmates, teachers, and other people connected to the girl, many instances pointed towards a girl suffering from mental health.

In 2010, when the girl was in junior high school she was found to have put various substances into other children’s school lunches including bleach, detergent, shoe polish, and benzene. This happened on many occasions and on one occasion, one of her classmates who she poisoned had to be treated at the hospital.

When the school investigated the case, the girl had said, “She told me she couldn’t understand why I was studying that much, so I got angry.” Rather than report the cases to police the city officials at the school felt, “the problem could be dealt with on the ground.”

In junior high school, the girl’s mother died of cancer. The girl also stopped going to school and it was reported that she only attended 3 days of the first semester of class. Her teacher would call or visit her home weekly to check up on her.

Just before she entered high school in March, the girl suddenly attacked and injured her father with a metal baseball bat while he was asleep. According to an acquaintance of the father, he was seen with bandages on his head. Police believed that the death of her mother and the remarriage of her father was the cause of the girl’s anger.

Her father and his new wife who also resided in Sasebo city felt she would be a danger to them and arranged for the girl to move into her own apartment. Though this incident was known to police, the school, and the welfare center in Sasebo, nothing was done.

The psychiatrist who evaluated the girl after she attacked her father, called a child consultation center in the city in June to warn that she might commit murder saying, “If she is left as she is, she could kill someone.”

According to the Japan Times, “Nagasaki prefectural officials said the center staff judged it would be difficult to take any measures because the psychiatrist declined to identify the girl due to privacy reasons.”

After the murder, the center officials contacted the psychiatrist and found out that the girl he was referring to was indeed the girl who ended up killing Aiwa. It was also revealed that the father of the girl had asked the psychiatrist to have her hospitalized the day before she committed the crime. The girl had confided to her stepmother that she wanted to kill someone. But the father’s request to have her hospitalized was rejected.

Arrest and Sentencing

The girl was taken into custody and questioned once police arrived at her apartment and found Aiwa’s body. She was taken into hospital to go through various medical examinations. After the murder, her father issued a statement apologizing to the Aiwa’s family saying,

“My daughter’s act can never be forgiven for any reason or cause. Aiwa had no time to experience the joy and happiness of life. When I think of the shock and sorrow felt by the bereaved family, it breaks my heart. I can’t find the words for an apology.”

Unfortunately, three months after the murder, the girl’s father was found dead in his apartment in an apparent suicide. Prosecutors said the girl showed signs of stress after her father’s death, but not any remorse for killing her classmate.

After a series of psychiatric evaluations, she was judged to be criminally responsible with prosectors explaining,

“because the girl had researched laws surrounding juvenile crimes at the library, and because she had purchased a weapon before the incident, she had meticulously planned the attack and was therefore criminally responsible for the murder of her classmate.”

However, the Nagasaki District Court’s presiding judge said, “the girl, who suffers from an autistic disorder, lacks any sense of morality and that sending her to prison would worsen her mental condition and make rehabilitation more difficult.” The girl was sent to a medical reformatory rather than tried in court.

Despite the culprit of the murder being caught and sent to a reformatory, sadly there was no happy ending. Justice may have been served but two young girls lost their future and a father took his life. The town had to face the failures of the education system, the breakdown of mental health support, and the deficiency of the public welfare structure.

The warning signs were missed, ignored, or not properly communicated. Hopefully, the city and country learned from this tragic series of events and are restructuring their approach to dealing with crime, mental health, and education.

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