When an 11-year-old girl walked back into her classroom at Okubo Elementary School in Sasebo, Japan, her clothes were soaked in blood. She looked at her classmates and said, calmly, "This is not my blood."

Minutes earlier, she had slit the throat of her 12-year-old classmate, Satomi Mitarai, in an empty room down the hall. The curtains had been drawn. No one heard anything.

How an Online Argument Became a Motive for Murder

The conflict between the two girls had started online. Satomi had called the younger girl "overweight" and "prissy" during a heated exchange on an internet forum the two shared. For an 11-year-old, those words landed like something much heavier than an insult.

The girl, identified only as "Girl A" to protect her identity as a minor, did not let it go. She planned. During the lunch break, she told Satomi she wanted to talk privately, and led her to an empty classroom. She had brought a box cutter from home.

What Happened After the Attack

Satomi Mitarai died from her injuries. "Girl A" was taken into custody and, following proceedings in the Nagasaki Family Court, was sentenced to two years of involuntary institutional commitment. That sentence was extended by another two years.

She was never tried as an adult. Japanese law at the time did not permit criminal prosecution for children under 14.

What the Case Changed in Japan

The murder, which became widely known as the "Sasebo Slashing," forced a national conversation in Japan about children, the internet, and the emotional weight of words typed on a screen. It was one of the earliest high-profile cases anywhere in the world to link online conflict directly to real-world violence among children.

Parents, educators, and lawmakers began asking questions they had not thought to ask before: What were children saying to each other online, and who was paying attention? The case led to broader discussions about emotional support systems in Japanese schools and the responsibility adults have to monitor children's digital lives.

Satomi Mitarai was 12 years old. She had called a classmate a name on the internet. She did not come home from school that day.