The "Sasebo schoolgirl murder" (佐世保女子高生殺害事件) refers to a case involving the slaying of 15-year-old Japanese high school student Aiwa Matsuo (松尾 愛和) on July 26, 2014. The slaughter transpired in the suspect's residence settled in Sasebo, Nagasaki Prefecture, Japan. 
Aiwa Matsuo was beaten with a hammer, asphyxiated, beheaded, and partially dismembered. Shockingly, Matsuo's suspected killer was her 15-year-old female classmate, whose name has been closely guarded by the police due to her age. In this case, we'll refer to the killer as Girl A.
Girl A was known as an ordinary and bright student. She kept up with her grades, participated in physical sports, and was considered to be profoundly intelligent compared to the average students in her school. Nevertheless, she definitely underwent numerous emotional breakdowns.
One of the main points displaying the start of Girl A's mental health decline was when she was in the 6th grade. In December 2010, she began to target students in the school by mixing foreign substances in the cafeteria food (Shoe cleaner, bleach, laundry detergent, etc.)
Girl A was eventually caught for committing these outlandish and hazardous acts, and the schoolmaster assembled all primary working staff along with cafeteria staff, informing them of these incidents and requesting them to keep a particularly close eye on her at all times.
Girl A's biological father was a reputable lawyer who earned his degree from a prestigious university settled in Tokyo. As for her biological mother, she was a member of the board of education in Nagasaki. Unfortunately, she would pass away from cancer in 2013.
The father would begin dating a young actress shortly after his wife's death and would eventually get married to her. Its speculated that this was the stage where Girl A's mental stability began to rapidly decline — and it wasn't tended to as seriously as it should've been.
After Girl A started attending Junior High School, her mental health proceeded to deteriorate further. She developed an immense interest in reading books about anatomy, medicine, and began catching cats to kill and dissect them for her own psychological gratification.
At one point, Girl A previously ruthlessly attacked her father with an aluminum baseball bat while he was sleeping. She managed to break his teeth and inflict other serious injuries. Nevertheless, the father did not wish to press charges against her for the vicious assault.
Once Girl A graduated to Senior High School, her father had about enough of her behavior and bought a separate residence just for her to live and sleep in. She also received tremendous financial support from him just so she could up-keep the apartment and feed herself.
Aiwa Matsuo and Girl A attended the same high school in Sasebo. Matsuo allegedly hung out with friends over the weekend and failed to return back home. Her parents grew concerned and reported her missing, consequently how the police discovered their daughter's battered corpse.
On the day of the murder, Girl A and Matsuo were shopping that afternoon when Girl A invited Matsuo to come over to the apartment she lived in and hang out more. Matsuo accepted the invitation; though unbeknownst to her, Girl A had a more diabolical scheme in mind.
After arriving at the apartment around 8 P.M. that very night, Girl A attacked Matsuo by bludgeoning her viciously with a hammer tool before strangling her to death with a dog leash and then wielding her hardware to administer unimaginable carnage to Matsuo's corpse.
It was at this time when Girl A used her tools, which consisted of a saw and hammer, to decapitate Matsuo, sever off her left hand, and slice her abdomen wide open to dissect her. This twisted experiment would continue on for hours until Matsuo's parents reported her missing.
A few hours later that night, at approximately 10 P.M., several ominous messages emerged on 2channel, which is a famous anonymous Japanese internet forum. These posts included seven grisly photographs, including a blood-soaked cloth and a series of images showing bloody hands.
The subject of the thread was, "I have ended up killing." It continued on, "Blood keeps pouring out even though even though I have wiped it away many times." Another message said, "Want to know what color the brain is? … I'll take good care of the brain and the spinal cord."
The next day, the police located Girl A's apartment and immediately executed a search for Matsuo, until they discovered her terribly mangled and decapitated corpse resting on the bed. Investigators also found the other tools used nearby the bed, and Girl A was taken into custody.
In a long series of interviews after the discovery of Aiwa Matsuo's body, Girl A confessed everything about the horrible murder that ended up shaking Japan to its very core. She reportedly informed police she "wanted to kill someone" and "wanted to dissect a dead body."
Girl A confessed to purchasing the hammer and saw, which was used in the gruesome murder. She also told detectives that she had experienced "dissecting cats" — which is one of the leading factors driving police to believe she needs to be psychologically evaluated.
Girl A's confession about taking the lives of cats on almost a daily basis proved to be factual after investigators further examined her apartment and made a petrifying discovery — a severed cat head in the kitchen refrigerator, along with Aiwa Matsuo’s head.
Girl A also apparently told her stepmother about her intense desire to murder somebody, and her father attempted to admit her into a psychiatric ward, though it failed. This particularly haunting occurrence transpired a few days before the brutal slaying of Aiwa Mutsuo.
Numerous specialists were distributed over the family court verdict to send Girl A (who turned 16-years-old shortly after the murder) to a medical reformatory rather than sending her back to prosecutors to be criminally indicted and imprisoned for this horrible crime.
The family of Aiwa Matsuo had also demanded severe punishment for their pain and suffering from losing her in such a brutal and undeserving fashion; however, the court declared that severe criminal punishment would not prevent her from committing another crime upon release.
Kenji Takeuchi, associate professor of juvenile law at Kyushu University's Graduate School, stated, "In prison, it is difficult to offer sufficient care in terms of psychiatric treatment. Long-term imprisonment is also harmful and may make it difficult to readjust to society."
In contrast, others have a very different view. Some experts dispute the effectiveness of this reformatory facility because it exclusively accommodates individuals up to 26 years of age. And, of course, others believe that a more severe sentence would have been sufficient.
However, in the Sasebo schoolgirl case, it appears that the court has taken Girl A's psychological deformities into consideration. The girl has a tendency to be hostile towards other people and has an extreme lack of empathy, resembling the traits of a primary psychopath.
After the decision, Aiwa Matsuo's father, who was in the courtroom, began to weep in his seat, carrying a photograph of her in his pocket. "That was not the decision I had expected. I can't accept it — I want her to continue apologizing to my daughter for the rest of her life."
The father of Girl A issued a statement apologizing to Aiwa Matsuo's family for his daughter's evil actions. He stated his daughter's act "can never be forgiven for any reason or cause." He also said he "was losing his confidence in his ability to continue living."
Months after the trial took place, the 53-year-old father of Girl A was found dead in an apparent suicide. He had hung himself in his own home settled in Sasebo. When Girl A was told about her father's death, she looked down shedding a single tear, and had said: "All life ends."
Despite there being very descriptive information regarding Girl A's personal life and family matters, unfortunately, there's not much information known about Aiwa Matsuo except that she was a model student who was polite, compassionate, and had a love for life and Karaoke.
This is the hearse carrying the coffin of Aiwa Matsuo leaving the packed funeral hall in Sasebo, on July 29, 2014. Aiwa's entire family, friends, and actually everyone from her school attended the funeral to mourn all together and say their final goodbyes.
