An 11-year-old boy, Adachi, disappeared after his stepfather, Yuuki Yamamoto, dropped him off near Sonobe Elementary School in Nantan, Kyoto prefecture, on 23/3. Adachi's mysterious disappearance sparked a nationwide search, involving over 1,000 police officers and firefighters.

Three weeks later, on 13/4, police found Adachi's body in a forest on a mountain, approximately two kilometers from the school. The boy lay on his back with no obvious external injuries, making the cause of death initially unclear. The subsequent police investigation uncovered several irregularities surrounding Adachi's disappearance, ultimately pointing to a sinister plot.

**Staged Disappearance and Misleading Clues**

On 23/3, Yuuki offered to drive Adachi to school, deviating from the boy's usual school bus routine. Instead of parking at the designated area, Yuuki stopped 200 meters away. Adachi was marked absent at the 8:30 am roll call, but due to the graduation ceremony, the school only contacted his mother at 11:50 am. Surveillance cameras confirmed Adachi never entered the school that day; no teachers or classmates saw him.

Upon notification, Yuuki called the police, claiming he had dropped Adachi off around 8:00 am. He actively participated in the search, distributing missing person flyers near the school the following day and contacting local firefighters for help. However, investigators soon found odd details. On 25/3, a shoe matching Adachi's was found along a mountain trail six kilometers west of Sonobe School.

Police search for the missing boy in Nantan, Kyoto. Photo: Yomiuri Shimbun

Adachi's backpack appeared on the mountain three kilometers west of the school on 29/3. This was peculiar because firefighters had thoroughly searched the area days earlier without finding anything. Adding to the suspicion, it rained on 25/3, but the backpack was dry, suggesting it was placed there after the rain. Police inferred that someone deliberately planted the items to mislead the search efforts.

**The Cover-Up Tactics**

Further investigation revealed more suspicious details linked to the 37-year-old stepfather. A review of Yuuki's car showed that some journey data from the day Adachi disappeared had been intentionally deleted. His phone records indicated multiple online searches for phrases such as "how to stop dashcam recording," "how to delete data," and "how to dispose of a body."

Security camera footage from a parking lot near the school on the day of the incident showed Yuuki walking alone, with no sign of Adachi. Confronted with the evidence, Yuuki confessed to police: "After taking Adachi to school, I drove to another location in the city and strangled the boy in the car."

By analyzing location data from Yuuki's mobile phone and car navigation system, police located Adachi's body on the mountain, approximately two kilometers southwest of the school, on 13/4.

Police investigate the area where Adachi's body was found, the evening of 13/4. Photo: Yomiuri Shimbun

The backpack and shoe, found earlier, were located three kilometers and six kilometers west of the school respectively, forming a triangle with the body's location. Police deduced that Yuuki had intentionally scattered these items in different directions to divert search teams and buy himself time. According to his testimony, Yuuki moved and hid the body at various locations after the crime to avoid detection. He monitored the search efforts, temporarily concealing the body in a public restroom just five minutes drive from Adachi's home before finally abandoning it on the mountain.

On 16/4, police arrested Yuuki on suspicion of abandoning a body. The investigation is ongoing.

Professor Yasushi Fujii of Meisei University's Psychology Department in Tokyo, stated in an interview with Fuji TV: "Yuuki's actions of actively reporting to the police and distributing flyers were tactics to construct a narrative covering his crime. By doing so, Yuuki transformed himself from perpetrator to victim and closely monitored the investigation to move the body when necessary."

**Strained Family Dynamics**

Following Yuuki's arrest, details about the family emerged. Yuuki met Adachi's mother, Ako, while working at an electronics factory in a neighboring town. Yuuki, a quality control section chief, was described by colleagues as "gentle, quiet, diligent, and good with computers." Ako was known for her beauty and outgoing personality.

Ako had divorced when her son was less than one year old. Yuuki also had a much older wife and a 10-year-old child. In 12/2025, Yuuki divorced and remarried Ako, adopting Adachi.

Police arrive at Adachi's family home, 15/4. Photo: Yomiuri Shimbun

After marrying, Yuuki moved into Adachi's home. Ako's parents initially opposed the marriage and were not officially informed when Yuuki moved in. Adachi's maternal grandmother once complained that Yuuki did not greet her when they met at home, finding her daughter's second husband untrustworthy but powerless as Ako always did as she pleased.

Adachi openly expressed his dissatisfaction with his new stepfather. He told classmates: "A strange man came to live at my house, they always argue, I hate him." When someone mentioned his stepfather's name, Adachi stated bluntly: "I despise my stepfather." A classmate of Adachi recounted witnessing Yuuki violently hitting the boy. When asked what happened, Adachi only replied, "Don't ask about my family."

On 19/3, days before Adachi's disappearance, Yuuki suddenly took leave, citing illness. On the morning Adachi disappeared, he contacted the factory again, saying that "something happened at home." The family of three had planned a spring break trip to Trung Quoc, with flight tickets booked for 24/3—the day after Adachi's disappearance.