On the last night of the year 2000, a killer entered the home of a sleeping family in Tokyo’s Setagaya ward and murdered all four of them. Then he did something no investigator had ever seen before.

He stayed.

For hours, the killer remained inside the house. He ate ice cream from the family’s freezer. He used the family computer to browse the internet. He bandaged a wound on his own hand using the family’s bandages. He slept on their couch. By the time he left, sometime the next morning, he had bled, sweated, urinated, and left behind enough physical evidence to convict any criminal twice over.

Twenty-five years later, no one knows who he was.

The Miyazawa Family

Mikio Miyazawa was 44, a marketing analyst. His wife, Yasuko, was 41, an English tutor. Their daughter Niina was 8 years old. Their son Rei was 6. They lived in a modest two-story house in Soshigaya, a quiet residential area of Tokyo’s Setagaya ward, in a neighborhood scheduled for demolition to make way for a city park. Their home shared a wall with Yasuko’s mother and sister next door.

On the evening of December 30, 2000, they were getting ready to celebrate New Year’s. Niina had recently received a present she was excited about. The family ate dinner together. Sometime late that evening, they went to bed.

The killer was already on his way.

The Night of December 30

According to the investigation that followed, the killer climbed onto the Miyazawa roof and entered through a small unlocked second-floor bathroom window sometime between 11:00 PM and midnight. He carried with him a sashimi knife he had purchased earlier that day at a Tokyo store.

He went to Rei’s room first. The 6-year-old was strangled in his bed. He never woke up.

The killer then moved through the house. He stabbed Mikio at the top of the stairs as the father tried to investigate the noise. He stabbed Yasuko as she came out of the bedroom. Then he descended into Niina’s room. The 8-year-old fought back.

By approximately 1:00 AM, the entire family was dead.

Inside the House After the Murders

What investigators would later piece together from the killer’s behavior after the murders is what makes the Setagaya case unique in criminal history.

He cut his hand during the struggle with Niina — severely enough that he bled throughout the house. He went to the bathroom and bandaged it with material from the Miyazawa medicine cabinet. He used the family computer. According to forensic analysis of the hard drive, he accessed websites for hours. He went into the kitchen. He opened the refrigerator and took out four cups of ice cream — pumpkin and melon flavors. He ate them.

He used the toilet without flushing. He took a long drink of barley tea. He removed his jacket and left it draped over a chair. He took off his shoes and walked through the house in his socks.

At some point, he lay down on the family’s couch and slept.

Sometime between 9:00 and 10:30 AM on December 31, he gathered some of his belongings — though he left most behind — and walked out the front door. Yasuko’s mother, who lived next door and shared a connecting passage, discovered the bodies later that morning.

The Evidence That Should Have Solved It

The Setagaya crime scene is one of the most evidence-rich scenes any modern investigator has ever encountered.

The killer left behind: his jacket, his sweatshirt, his belt, his neck scarf, his hat, his handkerchief, his fanny pack, multiple hair samples, fingerprints throughout the house, DNA from blood, sweat, and saliva, the murder weapon, the receipt for the murder weapon, multiple shoe prints in three different sizes implying he changed shoes, the toilet seat with biological material, and a fingerprint on the family computer that had been used for hours.

His DNA was sequenced and entered into every Japanese database. His mother’s mitochondrial DNA suggested a Southern European or Mediterranean heritage. His paternal Y-chromosome DNA suggested an East Asian origin, most consistent with a man from Korea or Northeast China. His shoes were a brand from South Korea. Sand found in his fanny pack came from the West Coast of the United States — specifically, samples consistent with the area around Edwards Air Force Base in California.

And yet: no match.

The Theories

Japanese police, working with the FBI, have pursued multiple theories over the years. None has produced an arrest.

The intruder theory. The killer was a stranger to the family — possibly mentally unstable or under the influence of drugs — who selected the house at random. This theory accounts for the strange post-murder behavior. It fails to explain the apparent planning involved in purchasing the knife.

The targeted killer theory. Yasuko had been working with parents in the neighborhood who were resisting the planned demolition that would erase their homes. Some of those parents had been involved in confrontations with city officials. This theory suggests the murders were a contracted hit by someone connected to the redevelopment. It fails to explain why a paid assassin would stay in the house.

The military theory. The sand in the killer’s bag, the specific brand of shoes, and his apparent knowledge of how to climb to a second-floor window without leaving easy trace evidence have led some investigators to speculate that he had military training, possibly American or South Korean. This theory has produced no specific suspects.

The runaway theory. The killer fled Japan within hours or days of the murders, returning to a country — most likely South Korea or the United States — where Japanese investigators had no jurisdiction and limited ability to pursue him.

Why It Remains Unsolved

In most countries, a crime scene this rich with evidence would have produced an arrest within months. The Setagaya case has gone unsolved for three reasons.

First, Japan’s national DNA database remains small compared to those in the United States or much of Europe. Without a database match, even a perfect DNA profile leads nowhere.

Second, the apparent mixed ethnicity of the killer suggests he may not have been Japanese-born, complicating any database search confined to Japanese nationals.

Third, and most importantly: the killer almost certainly left the country. By the time police understood what had happened in that house, he was likely already on a plane.

25 Years Later

The Setagaya Police Station maintains an active investigation. Every December 30, officers gather to renew their commitment to the case. A specific detective is assigned full-time to keep the file alive.

In 2011, Japanese investigators traveled to the United States to share evidence with the FBI in hopes of a database match. None was found. In 2016, the case was profiled internationally in an effort to surface new tips. None proved fruitful.

In 2023, the Metropolitan Police Department released digitally reconstructed images of the killer’s possible appearance based on his DNA, hair, and physical evidence. The images received widespread coverage. No verified leads followed.

The killer, if alive, is now likely in his late 40s or 50s. He could be living anywhere in the world. He could be dead.

A Family Still Remembered

Mikio. Yasuko. Niina. Rei.

They were a family who valued community, who fought for their neighborhood, who hosted English-language classes in their living room. The home where they were killed was demolished in 2013, replaced by the park that the redevelopment had always promised. A small memorial stone marks the spot.

Every year on the anniversary, Yasuko’s mother and sister still visit. Twenty-five years on, they continue to wait for an answer that may never come.

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