Yoshitomo Hori was born on April 29, 1975, in Toki, Gifu Prefecture, Japan. He was the fifth child of a Zainichi Korean father and a Japanese mother. Initially, he was a Korean citizen, but he and three of his brothers were naturalized as Japanese citizens on August 22, 1984.

When he was just six months old, Hori was diagnosed with purpura, a medical condition that required him to be hospitalized for several months. He continued to have regular medical check-ups until he was about five or six years old. His father worked as a dump truck driver, but he was often violent and had many arguments with Hori's mother, especially over his affairs with other women. Because of this instability at home, Hori and his siblings sometimes felt neglected. As a result, his mother enrolled him in nursery school.

When Hori was around seven, his father moved the family to Nagoya, Aichi Prefecture, but he continued his affairs. In April 1982, as Hori was about to enter elementary school, his father divorced his mother and moved in with another woman. Following the divorce, Hori went to live with his paternal grandmother, with whom his mother had a troubled relationship.

In April 1985, after Hori completed the fourth grade, his father joined a local criminal group due to financial difficulties. This led to Hori's family moving to a housing estate in Nagoya. At this new school, he developed an interest in soccer.

When Hori attended junior high school, he was disappointed to find that there was no soccer club. He asked his mother to transfer him to a different school, but she could not afford it. He eventually joined the tennis club instead and dedicated himself to the sport, even when he had the option of traveling by bus to the soccer club at another school. During his first summer vacation in high school, one of his brothers offered him a part-time job in construction to help him buy a new tennis racket, which he accepted.

Over time, Hori struggled in school. He was often punished by a math teacher for wearing torn pants from work. Eventually, his behavior led him to become a delinquent, skipping classes and bothering fellow students. Hori eventually dropped out of school to work for one of his brothers.

After graduating from junior high school in 1991, Hori attended high school part-time but dropped out due to lack of interest. He returned to work odd jobs for his brothers and became involved with a woman named Kou, an employee at a local snack bar. They got married after she became pregnant, but their life together faced many challenges.

Hori continued to have multiple relationships and faced financial troubles. His chronic back pain affected his ability to work, and he fell into debt. Eventually, he was kicked out of his house due to not paying rent, leading him to move in with different women.

Around May 1998, Yoshitomo Hori, who had changed his surname from Kim, became desperate for money. After failing to pay a car loan, he thought about committing small crimes. He first considered purse snatching but switched to robbing pachinko parlors. Hori planned to break into a parlor after closing time. After preparing tools, he went back and followed the parlor's manager, 45-year-old Kazuo Magoori, to his home. He surveyed the house during the day and then pretended to know the manager. On June 28, 1998, he entered the Magoori residence with an accomplice. Once inside, they killed the couple and stole valuables.

After this incident, Hori’s life continued to spiral. His wife filed for divorce, fearing his behavior might draw police attention. Following the divorce, Hori lived with Hinoe but later ended up vandalizing vending machines with another accomplice, Sato. Soon, his relationship with Hinoe ended due to theft, leaving him homeless. He moved back with his parents and worked for his older brothers in construction.

Hori's life took another turn after moving in with his girlfriend, Otsu. She became pregnant, which made Hori anxious about his previous crimes being discovered. Otsu had a miscarriage, leading to her developing a panic disorder. Hori then spent more time gambling. By July 2006, due to issues with his back pain and a fight with his brother, Hori quit his job.

On July 20, 2007, Hori remembered a house he worked on that was occupied by a 69-year-old woman in Moriyama. He went there with Sato, pretending to conduct an inspection. They wrapped the woman’s face and neck with tape and seriously injured her. She later required hospitalization but survived. They stole cash and items from the house.

Back in Nagoya in August 2007, Hori met another man, Kenji Kawagishi, as well as two others. They discussed robbery ideas and planned to abduct office workers. On August 24, they abducted 31-year-old Rie Isogai while pretending to ask for directions. They took money and her credit card and later killed her in a forest.

Afterward, one of Hori’s accomplices confessed to the police. Hori was arrested on August 26, 2007. He and his partners confessed to their crimes during detention. The trio faced multiple charges including murder and robbery.

During the trial, prosecutors argued for the death penalty due to the severity of the crimes. Hori was sentenced to death, while his accomplices received life sentences. After appealing, his sentence was commuted to life imprisonment in 2011. However, he was later linked to the murders of Kazuo and Satomi Magoori through DNA evidence. In 2012, he was again sentenced to death for their murders by a different trial. Hori's appeals against the second death sentence were ultimately dismissed, finalizing his penalty.