Evidence led police to the notion that the killer, instead of fleeing immediately after killing the Miyazawa family, had decided to stay in the house as an unwanted house-guest. He hadn't even gone through the trouble of covering up the four family member's bodies, but decided to make himself comfortable for the evening.

The unsub had apparently napped on the family's living room sofa, which was one of the oddest developments in the story itself. Usually, suspects flee from the scene as soon as they can, as each minute increases the odds of being discovered, but this killer had seemingly savored the intimacy of living in his victim's home for a night.

The killer of the Miyazawa family had helped himself to food from the family's fridge, namely ice cream. Police would eventually discover four ice cream wrappers, also referred to as popsicle wrappers in some of the sources, with the supposed killer's fingerprints on them. These fingerprints matched up with other fingerprints left all over the house, which didn't belong to any of the family members present.

This unsub had also used the family's computer, which was located in the downstairs study. They discovered that the computer had been accessed in the early morning of December 31st, specifically at 1:18 AM, an hour or two after the family was likely murdered. The unsub had visited a website previously bookmarked by Mikio, belonging to the Shiki Theater Company. You see, Mikio had a history of working with theater as it had been a passion of his, so one has to wonder if this was some kind of sick joke on behalf of the killer, or perhaps even the family was murdered hours after many believed them to be.

However, at 1:18 in the morning, someone had visited that website and attempted to buy tickets for a show online, and the odds remain heavily stacked in favor of the killer doing so.

The killer had apparently also logged on hours later, at approximately 10:05 in the morning, to browse the websites of Mikio's company, Interbrand, and the school that Yasuko taught at. Strangely, the killer only browsed websites the family had bookmarked, perhaps to try and relish being in the intimacy of their home.

After using the computer for a grand total of ten minutes, the killer had then unplugged the computer from the wall.

Throughout the night, the killer had gathered an assortment of the family's ID and credit cards, which were all found sorted in the family's living room, nearby the sofa that the unsub had slept in. This was very odd, and many have theorized that this was an attempt by the killer - or killers - to try and guess the PIN codes needed to use the cards. Once he left the scene, he was unlikely to try and keep guessing and risk exposure, so he left them behind.

Before leaving, the unsub had also gathered an odd variety of the family's belongings and garbage, and put them in the bathtub - for whatever reason. These items were mainly garbage, such as ice cream wrappers or advertising leaflets that had been cut up, but also contained some of Mikio's work receipts and Yasuko's school documents, along with some feminine sanitary items that contained the killer's blood. Many have wondered exactly why the killer would leave such an odd grouping of junk in the bathtub, but have figured that he maybe meant to do something with them and just forgot. Perhaps he had meant to let the items soak before being discovered, in an attempt to hide evidence, unaware that he had left boatloads of it throughout the house.

After sleeping in the Miyazawa home for a few hours, police suspected that the killer had stolen some money from the family, approximately one-hundred-and-fifty-thousand yen. That's roughly the equivalent to over a grand, in American currency. However, the investigators were able to easily find more money in the family's study, where the killer had been eating ice cream and using the computer, leading them to think that this wasn't a simple robbery.

Also, if this had been a robbery, the killer might have stolen some valuables, but it looked like the family's belongings were all left behind. The only item believed to be missing was an old jacket, which had belonged to Mikio, but that was it.

When Yasuko's mother had entered the crime scene, she had recalled the front door being locked. This led police to think that the killer had left in another way, perhaps back through the second-story bathroom window he entered. But over the years, Yasuko's mother has become less-than-certain that the door was locked when she arrived, and it has never become absolutely clear how the killer left the scene of this heinous crimes.