Kiyoshi Ōkubo was born on January 17, 1935, in Takasaki, Gunma Prefecture, Japan. He was of mixed heritage, being one-quarter Russian. His mother was half Russian and half Japanese, and she cared for him deeply throughout his life, even as he grew older.

Kiyoshi's early life was marked by bullying. After the Pacific War began on December 8, 1941, he faced mistreatment from other children. This period of his life was challenging and likely contributed to his struggles later on.

In his late teens, Kiyoshi began engaging in criminal behavior. On July 12, 1955, he committed a serious crime. Later that year, on December 26, he attempted to commit another crime but was unsuccessful. After this attempt, he was arrested and spent time in jail. Kiyoshi was released on December 15, 1959.

In 1960, he made an attempt to commit another crime on April 16, but again, he was unsuccessful. However, the victim decided not to pursue the charges against him. On May 5, 1961, Kiyoshi got married and had a family, including a son and a daughter.

His behavior continued to escalate. On June 3, 1965, he threatened a man. He then raped two women on December 23, 1966, and February 24, 1967. Kiyoshi was eventually imprisoned on June 7, 1967, and was released on March 3, 1971.

Between March 31 and May 10, 1971, Kiyoshi Ōkubo killed eight women in Japan. His victims were young women aged 16 to 21. The women he murdered included Miyako Tsuda, Mieko Oikawa, Chieko Ida, Seiko Kawabata, Akemi Sato, Kazuyo Kawaho, Reiko Takemura, and Naoko Takanohashi.

On May 13, 1971, a 21-year-old woman went missing. Her brother searched for her and eventually located Ōkubo. The police apprehended him on May 14, 1971.

After his arrest, he was put on trial. On February 22, 1973, the district court in Maebashi sentenced Ōkubo to death by hanging. He did not appeal the decision. Kiyoshi Ōkubo was executed on January 22, 1976, in the Tokyo Detention House. Reports stated that he was unable to stand on the day of his execution.