He ate four containers of ice cream from their refrigerator. He used their computer to browse the internet. He may have napped on their sofa. And somewhere before dawn on December 31, 2000, the person who had just murdered an entire family in the quiet Kamisoshigaya neighborhood of Setagaya, Tokyo, walked out the back door and disappeared. More than two decades and 246,000 investigators later, nobody knows who killed Mikio and Yasuko Miyazawa and their two young children. The case is Japan's most infamous unsolved crime, a forensic puzzle that has produced mountains of evidence and zero arrests.
The Miyazawa family lived in a two-story house adjacent to Soshigaya Park in the western suburbs of Tokyo. Mikio was 44, his wife Yasuko was 41, their daughter Niina was eight, and their son Rei was six. On the night of December 30, 2000, sometime between 11:30 p.m. and just after midnight, someone entered the house through a second-floor bathroom window at the rear. Investigators believe the intruder climbed the park fence, stepped onto an air conditioning unit, and removed the fly screen. Six-year-old Rei, sleeping in his upstairs room, was strangled first. Mikio apparently confronted the intruder and fought him, sustaining stab wounds from a sashimi knife whose blade broke off inside his head. The killer then attacked Yasuko and Niina with the broken knife and finished the assault with a santoku knife taken from the family's kitchen.
What makes the Setagaya case uniquely disturbing is what happened after the murders. Rather than flee, the killer stayed in the house for hours. He treated his injuries with the family's first aid supplies -- Mikio had wounded him during the struggle. He consumed four containers of ice cream, several bottles of barley tea, and melon from the refrigerator. At 1:18 a.m., he logged onto the family computer on the first floor and browsed the internet. He used the toilet without flushing. Some investigators believe he may have slept on the sofa. He left before dawn on New Year's Eve morning. The sheer brazenness of this behavior baffled investigators, suggesting either extraordinary coldness or a psychological profile far outside the norm.
For all his time inside the house, the killer left an extraordinary volume of physical evidence. Blood analysis revealed Type A blood that did not belong to any family member, confirming the intruder had been injured during the attack. DNA analysis determined the killer was male and possibly of mixed heritage: maternal DNA suggested European ancestry, possibly from a Southern European or Caucasus region country, while paternal DNA indicated East Asian descent. The Y-chromosome showed Haplogroup O-M122, common among East Asian populations. Only 130 units of the killer's distinctive shirt were ever manufactured, and police tracked down just twelve of the buyers. His shoes were made in South Korea but marketed under the British brand Slazenger. Despite this wealth of forensic detail, no match has ever been found.
The Setagaya investigation became one of the largest in Japanese history. Over 246,044 investigators have worked the case, collecting more than 12,545 pieces of evidence. As of 2021, a 20-million-yen reward remains active. In 2015, forty officers were still assigned full-time. The house itself, deteriorating with age, was eventually slated for demolition after police confirmed all interior evidence had been preserved. In 2023, ten high school students broke into the site on a dare, leading to prosecution under Japan's Minor Offenses Act. A mysterious Jizo statue appeared at the nearby Sengawa River one hundred days after the murders, and investigators have never fully explained its origin. In 2024, the Setagaya Ward Assembly pushed for expanded DNA evidence laws, and advocacy groups petitioned for national guidelines on forensic DNA use -- changes driven in part by the enduring frustration of this single unsolved case.
Kamisoshigaya remains a quiet residential area on the western edge of Tokyo, the kind of neighborhood where families walk to the park and children ride bicycles on tree-lined streets. Soshigaya Park, directly behind where the Miyazawa house stood, is still used daily by local residents. The ordinariness of the setting is what makes the crime so unsettling. This was not a dark alley or a remote location but a family home beside a public park in one of the safest cities on earth. Each December, as the anniversary approaches, Japanese media revisit the case, and police renew their appeals for information. The killer, if still alive, would now be in his forties to sixties. The evidence waits in storage, preserved and re-examined with each advance in forensic technology, a case that Japan refuses to let go cold.
The Miyazawa residence site is located at 35.656N, 139.599E in the Kamisoshigaya neighborhood of Setagaya, western Tokyo. From the air, Setagaya appears as a low-density residential district with abundant tree cover, bordering the Sengawa River. Soshigaya Park is visible as a green patch adjacent to the former crime scene location. Best viewed below 2,000 feet. The nearest airport is Tokyo Chofu (RJTF), approximately 4 nm to the west. Tokyo Haneda (RJTT) lies about 10 nm to the south-southeast. The area is under Tokyo approach airspace, so altitude restrictions may apply.