Setagaya Family Murders Workbook + Theories Discussion
Hey everyone! First time posting on reddit.
I've been heavily captivated by the Setagaya family murder case for a while now. I decided to make an excel spreadsheet workbook, consisting of all the key details and evidence regarding the case. *I can't attach files on reddit apparently, so Iinked a google spreadsheet instead.
https://docs.google.com/spreadsheets/d/1aBIVV0KmYH5owvrIdevkAXzgEiH3-gKH/edit?usp=sharing&ouid=117712921993243648668&rtpof=true&sd=true
For anyone unfamiliar with this case - on Dec 30th of 2000, the Miyazawa family of four was murdered in their own home.
The killer was never caught, despite leaving tons of physical evidence (fingerprints, hair, clothes, etc) at the scene while lingering in the house accordingly for a few hours, almost displaying domestic comfort (using the family PC, napping, eating ice creams, even using their toilet) during his post-murder stay.
While going over the abundant information spiraling around this case, I wanted to organize the info into a workbook, so anyone interested in this case can easily access them.
The source that I used while gathering the info is the Japanese Wikipedia article on the case.
I know that Wikipedia is not really a credible source, but this article is substantially cited with official Japanese newspapers and reports - you can check the source alongside the info as well. Plus, the English-based articles on this case are, a lot of the times, misinformed, so I've recently been only checking over Japanese sources and decided this particular article is the best option.
Information in the excel spreadsheet workbook is categorized into 9 sections, including Case & Victims, Perpetrator Behavior, Evidence - Sand & Trace and etc. I've input everything in the Wikipedia article into Claude AI and had it organize the information into one workbook.
Hope this helps anyone wanting to refresh their memory, or just finding out about this case!
*This workbook itself might not be 100% accurate either - cross-checking is always encouraged!
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Now, I would love to discuss with you about who the perpetrator might be!!!
The most popular theories seem to be 1. Korean national and 2. Someone linked to the Edwards AFB & US military background.
I personally disagree with both of the theories.
The only item linking the perp to the Korean angle is the Slazenger shoes (because the 280 Korean size pairs were only manufactured in Korea, and not officially sold in Japan at the time). But the perp could have purchased it at a parallel-import market in Tokyo (they were huge back in 2000), thrift stores, or had them delivered as well. There are many other possibilities and routes of acquiring those particular shoes than the validity of marking the perp Korean.
Plus, the perp's fingerprints were run through the Korean fingerprints database and none of them were a match. South Korea records all their citizens' fingerprints when they turn 17 by law - to create their resident registration card (it's literally printed on the card itself). TMPD in their 2025 findings clarified that the perpetrator was in his 30s at the time of the crime, so if he was Korean, his fingerprints must have been registered in the database and triggered a match. They also started recording fingerprints of everyone who travels in and out of Korea - this was said in Nicolas Obregon's podcast on this case 'Faceless', but it's only been that way since 2012, so if the perp had visited Korea prior to the murder and acquired the Slazenger shoes, we would not be able to know by his fingerprints data. So that's the only thing keeping me from ruling out the Korean angle.
The second theory - someone from the US with military background. I do not think this is valid either.
The only evidence linking the perp to the US military is the sand found in the hip bag he left behind. The sand is known to be from California - specifically resembling sand found near the eastern part of Edwards Air Force Base.
But sand from Miura peninsula, Kanagawa were also found inside the hip bag & in the pocket of the Uniqlo jacket. I honestly think the California sand is a red-herring. The perp could have gotten the hip bag through parallel-import markets, thrift stores, etc - again, same with the Slazenger shoes. I believe the Miura peninsula sand is more of a clue than the California sand is, because the Miura sand is more likely to have been a byproduct of the perp's usage of hip bag than the latter.
The reluctance from the TMPD to dig into the Edwards AFB lead is quite interesting too, though. In Nic Obregon's podcast, it was confirmed that the TMPD never traveled to that area or asked for investigative assistance to police in California. I believe the TMPD deemed it's not worth looking into, since it would be too much work despite the insufficient supporting evidence.
I also believe the killer acquired those foreign-based items (shoes, hip bag) off secondary markets (parallel-import, secondhand items etc).
If you look at the TMPD's official 2026 case details page on their website and navigate to the perpetrator's items - you see the green scarf. The low quality scarf, its manufacturer and retailer unknown. Two tips consistently say they acquired the same scarf as a prize, at a clothing store and a gas station - so it's possible the perp had gotten it as a prize as well.
Someone who wears a low-quality scarf with no tag given as a free prize - I can kind of picture the same person going to gray markets in Tokyo and shopping used, secondhand items for a cheap price. But this is speculation on my part. Looking at the the perpetrator's entire outfit-from the bucket hat and the budget Uniqlo jacket to the heavily washed raglan shirt-it feels off and budgety. I feel like the perp was a 30s dude living on his financial margins - wearing whatever cheap scarf he won as a prize.
I am talking too much, but I am really passionate about this case and just want the killer to be caught already. I hope the victim's family, especially Setsuko (Mikio's mother) finds peace after all these years.
One more speculation - I think the perp was a mentally unstable local Japanese male in his 30s - possibly linked/adjacent to the skating world.
Setagaya is a suburban area - yes it is Tokyo, but really in 2000, not many foreigners traveled to that specific area of Setagaya. It was a suburban residential neighborhood, the only possible tourist attraction being the Soshigaya park - directly adjacent to where the Miyazawa household was located.
At the time of the murder, only 4 homes were still in the neighborhood. If you take a look at the TMPD's official aerial photos 1 and 2 here, the block of the Miyazawa household looks isolated, surrounded by nothing but empty land. If a mentally unstable sicko was looking for a target to murder, that exact household provides the perfect environment to be honest. Some people say the neighborhood was very lively at the time, but looking at the aerial photos of the area, it's likely that the isolation of the household made it vulnerable, especially at night.
The only relational clue we have on this case is the dispute between Mikio Miyazawa and the skaters at the Soshigaya park. At the time, the Soshigaya park had skaters from all over the country - according to Masafumi Kajitani (a renowned skater from Japan long ago) on Nic Obregon's podcast. He also stated that the park had a positive atmosphere - not much trouble with the residents, but one time he heard that one of his friends had a clash with Mikio Miyazawa. Maybe the perp was one of the traveling skaters who witnessed the dispute? After finding out about the Miyazawa household's location and its isolation, he started sizing up his murder plan?
I know I am speculating here, but I honestly believe the perpetrator was a Japanese. Why he has not been caught yet? He never committed a crime after that to be registered onto the database, AND Japan's strict laws on utilizing DNA for criminal investigation tremendously hinder progress!
Former Chief of the Setagaya murder investigation, Takeshi Tsuchida, stated that it's illegal for the Japanese police to even inquire about DNA usage to foreign police - so we can assume how conservative they are when it comes to handling DNA and privacy problems. It's very unlikely they will make an exception for this case, and it's even more unlikely they will change their legal frameworks anytime soon.
People say IGG (Investigative Genetic Geneology) could solve this case just like how they caught the Golden State killer, but I believe this will be significantly less effective when it comes to finding individuals of Asian descent. Consumer DNA databases are overwhelmingly European. If the perp does not have close or distant relatives in this system, it's impossible to generate a family tree in the first place. Plus, commercial DNA testing is almost non-existent in Asian cultures - I know this for a fact - almost nobody does this, like ever. But the Mitochondrial DNA of the perpetrator was reported to be Southern European - redetermined in 2025 to include the Caucasus or eastern Arabia. This might be of help, but seriously, we do not know how relevant this DNA information is. We do not know how many generations back this mitochondrial DNA date to. I am not an expert in forensics, so I would love any insights on how to catch him through forensic investigation (even though Japan's laws won't allow the police to do it).
The more I talk about this case, the more I get frustrated because there's just no way of catching him as of now - unless some unbelievably quick changes in Japan's legal frameworks on handling DNA and forensic breakthrough happen.
Thank you for reading, hope you guys check out Nicolas Obregon's Podcast Faceless - he presents some of the most extensive and credible information.
Any discussions and insights are all welcome! I really want to hear what you guys think of this case, now that it's gone absolutely cold.