He Killed His 21-Year-Old Neighbor Then Himself

The tragic story of the murder-suicide of Momona.

Momona was like most 21-year-old girls in university. She liked taking selfies and posting them on Instagram, she liked shopping and eating fast food. She enjoyed going to restaurants and cafes with her friends and dressing in the latest fashion trends.

From high school until her time in university, she was always doing something. And though she was a busy body and very social, she was also described as kind, considerate, and concerned with the well-being of those around her. She enjoyed her school life and was looking forward to a good future.

However, all that ended on April 28th, 2021 when a man named Satoru Komata, the man living below her, decided to break into her apartment, hit her repeatedly with a crowbar, stab her and leave her as she bled out. What he did after was even more unbelievable.

Why was Momona targeted? Did the two know each other? What happened in her apartment and how did Satoru kill himself? This is the story of the murder-suicide in Osaka Japan.

“He was sensitive to household noise.”

What We Know About Satoru

This incident occurred in Osaka at the end of April 2021 so there is still information either not reported by the media or still forthcoming. What we do know about the incident is the man who lived on the second floor below Momona was named Satoru Kamoto.

He was a 48-year-old man originally from Shimane Prefecture in Japan and had been living in the building since 2016. An article from Yahoo News reported, “he graduated from a local high school and got a job related to livestock. After that, he worked at a gas station and a transportation company, but it didn’t last long.”

Sankei News reported that he belonged to a building maintenance company located in Osaka. Being dispatched to different areas, he had been residing in the apartment for 5 years before the incident. A coworker from one of his jobs noted, “he had a serious and quiet personality.” He was also reported as being very punctual and regimented as he was never absent or late from work.

But despite seeming like a normal, serious, middle-aged adult, there was something about Satoru that made him angry and enraged. He often complained about noise in the apartment building. In an article by the Tokyo Reporter, a relative of Satoru told police that, “He was sensitive to household noise.”

There had actually been a complaint made by Satoru about the tenant living next to Satoru on the 2nd floor. At the beginning of April 2021, Satoru started banging on the wall of this tenant who was a man in his 20s. The banging lasted for hours and continued for days.

The neighbor told police that he wasn’t making noise and was often asleep when the banging would begin. He didn’t understand why Satoru was complaining about the noise when the man was being quiet and usually sleeping as the banging came from midnight until morning. He told police,

“I was terrified by the wall relentlessly being banged. I thought I might have been attacked, and I was trembling. It wouldn’t stop.”

The man also said that even when he would greet Satoru in the hallway, he would be ignored. The man told police he didn’t hear much noise from other apartments including Momona’s place. Afraid of Satoru, the man moved out of the apartment in April. And soon after that, Satoru found a new target.

“We had plans to go for a drive once the state of emergency was over…”

What We Know About Momona

Momona Yoshioka was born and raised in Kyotango City, Kyoto, and moved to Osaka to attend Sangyo University in 2018. According to Iza News, a female classmate of hers said, “She was always thinking of others and never complained or had anything bad to say about anyone.”

She moved into a 26-year-old steel structure called the Takashi Heights Apartments complex on the third floor in 2018 when she started going to school. She lived in a small one-room apartment which cost around 40,000 yen or $400 a month.

Living away from her family and on her own for the first time, she tried to make as many friends as possible. Her Instagram showed pictures of her with her friends hanging out around the city or cooking Japanese food in her home.

In high school, Momona was part of the student council and athletic association so she wanted to continue to stay active in her school. Momona became the manager of the boy's soccer team at the university so she could increase her circle of friends. Staying with her male and female friends gave Momona a sense of connection and safety that she needed because she was away from her family.

However, at the age of 21, in her fourth year of university, Momona would find out that she wasn’t safe. Not even in her own home. According to Yahoo News, Satoru, who complained of noise, must have focused his attention on the upstairs apartment after the man next door moved out. No one really knew if there had been any connection between Momona and Satoru.

There hadn’t been any official complaint filed and a neighbor of Momona said, “Sometimes she had friends over and I could hear voices but it wasn’t anything too loud. It didn’t seem like it would bother anyone.”

“I heard a woman screaming ‘Mom! Mom!’ about 5 minutes ago”

-emergency call to police from neighbor

The Crime

On the morning of April 28, 2021, calls came to the police from concerned neighbors who heard screaming from the third floor of the apartment complex. “I heard a woman screaming ‘Mom! Mom!’ about 5 minutes ago,” said one of the neighbors who called 110, the equivalent of 911 in Japan.

According to NHK News, police rushed to the scene and found that Momona’s door was unlocked but had a door stopper placed on the floor as well as adhesive tape from the outside of the door making it impossible to open from the inside. Once the police entered her apartment, they found Momona lying on the floor covered in blood.

Mainichi News was able to confirm that there were multiple stab wounds and blunt force trauma on the back of the head possibly caused by a crowbar. Momona was taken to hospital but died of blood loss from the wound on her head as well as deep cuts to her thigh which hit an artery. Dozens of knife wounds were found on her legs and back and bloodstains were seen from the living room to the entrance.

Police found a crowbar, kitchen knife, as well as a handmade spear that had a 60 cm or 23-inch wooden pole with a knife attached to it using wire. As the police were finding Momona’s body, suddenly a fire broke out directly from the apartment below.

Momona’s balcony door was unlocked and there was a ladder going from her balcony to the balcony below. The apartment building has ladders on each floor in case of emergency situations like earthquakes that are quite common in Japan.

When police went down to the second floor to investigate they found that Satoru had doused himself with kerosene and lit himself on fire. He was taken to the hospital but was pronounced dead. His cause of death was listed as carbon monoxide poisoning.

Planned Attack

Witnesses saw a man, who seemed to be Satoru, climbing down from the third-floor apartment and entering the second-floor apartment minutes before the fire erupted. NHK also reported that Satoru’s fingerprints were found on the weapons found in Momona’s apartment.

Police also found multiple receipts in Satoru’s apartment for the crowbar, wooden stick, kerosene, and other items purchased just a few weeks before. Security cameras at a nearby hardware store showed a man who resembled Satoru purchasing the items.

Although there was no connection found or any evidence that Momona and Satoru had ever exchanged words, a police officer said,

“The situation at the scene suggests a strong murderous intention toward the woman, but the death of the man makes it difficult to clarify the motive.”

Since Satoru died before he could explain his reasons, we may never really know the true reason he targeted Momona. Was he angry because of noise coming from her apartment? Was he frustrated from his work, life, or personal issues? Was there some link to mental illness and his “noise sensitivity” issues? Or did he have some personal vendetta against Momona?

According to Professor Mafumi Usui (Criminal Psychology) of Niigata Seiryo University Graduate School,

“It is not uncommon for noise in the neighborhood to become a problem. If there is noise, usually people consult with the management company. But for someone with a mental issue, they might not be able to confront the issue directly. Instead, you do anything to escape from the unpleasant situations and some people will take extreme actions.

It’s difficult to prevent it because you can’t choose the residents in your neighborhood. There is no way to prevent an incident like this one that happened without any warning. It’s scary to think that anyone anywhere can be involved in a similar crime.”

Satoru might have not been able to communicate his frustration and instead of dealing with issues like noisy neighbors logically by calling the landlord or the police, instead, he felt the need to trap Momona in her apartment, break-in with three weapons, kill her and then return to his apartment to kill himself. Had Satoru or someone around him been able to get him help and someone to talk to about his bottled-up frustration, things might have turned out differently. Unfortunately, in this case, a young, lively, positive woman lost her life.

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