KITAKYUSHU -- A man arrested in connection with the Dec. 14 stabbing of two students at a McDonald's restaurant in this southwestern Japan city that left a 15-year-old girl dead had become isolated from his neighbors, running into trouble over noise issues after divorcing over a year earlier, it has been learned.

However, a week after the arrest of 43-year-old Masanori Hirabaru on suspicion of attempting to kill a 15-year-old boy injured in the attack, the motive for the assault on the teens, whom he did not know, remains unclear. Fukuoka Prefectural Police are trying to unravel the background to the incident and what drove the assailant to commit the crime.

When Hirabaru's home was shown on a TV news report, a woman in her 60s working at a real estate firm in Kitakyushu was taken aback.

"I was surprised as it was showing a house I had seen before," she said. In April 2024, about eight months before the stabbings, Hirabaru had called her company to inquire about selling his home. He lived in a wooden two-story house located in a residential district of Kitakyushu's Kokuraminami Ward, about 1 kilometer away from the McDonald's restaurant. He asked the real estate firm about the market prices of homes in the area, so the company checked the register and checked the house's exterior.

The company provided a market price by phone the following month and told Hirabaru that to sell it, they would need to check inside and confirm the deed to the property, but they never heard back from him. The company didn't hear why he wanted to sell the home.

Around the same time, the prefectural police started to receive complaints from residents about noise Hirabaru was making.

"I heard sounds of firecrackers going off as early as 6:30 a.m.," a man in his 70s who lives nearby said. Hirabaru is believed to have been throwing firecrackers from a window. The neighbor also heard shouting through a loudspeaker, and said that one time, Hirabaru played military-sounding music from his vehicle at high volume. Police also received complaints in October, and it is believed that Hirabaru became increasingly isolated.

Sources close to Hirabaru said that the land the house was on and which he was trying to sell was a gift from his mother in 2006. He had married and lived with his wife and child for some time, but investigative sources said that he divorced over a year ago, and is believed to have been living by himself.

According to the manager of a store in Kitakyushu selling replica guns and other items, Hirabaru had started coming in several years ago, making several purchases a year including a replica gun costing over 10,000 yen (about $64) and imitation swords costing tens of thousands of yen (over $100) apiece. He once bought two knives, but the store said he had not been in since summer this year. "He was an extremely quiet person," the manager reflected.

Hirabaru was raised in Kokuraminami Ward and graduated from elementary and junior high schools in the city. At high school he belonged to the basketball club. Sources close to him said that his relatives were wealthy, owning multiple apartments and land. According to one of his acquaintances, Hirabaru was the youngest of four siblings, and seemed reserved.

"He was a really gentle child. I can't associate him with the incident," said a 58-year-old man who knows Hirabaru.

(Japanese original by Hibiki Yamaguchi, Emi Izuchi and Akiho Narimatsu, Kyushu News Department)