Okubo was born in Gunma prefecture on January 17, 1935. He had convictions for rape going back to the 1950s and had served several sentences. He drove a white sports car, dressed as an artist, and told women he stopped in the street that he was a painter and wanted them to sit for him. He also used the name Watanabe Kyoshi.
Between March 31 and May 10, 1971 he killed eight young women aged sixteen to twenty-one: Miyako Tsuda, Mieko Oikawa, Chieko Ida, Seiko Kawabata, Akemi Sato, Kazuyo Kawaho, Reiko Takemura and Naoko Ishizaka. He raped them and strangled them, and buried the bodies in fields and woodland in the prefecture. Forty-one days for eight victims is one of the most compressed series on record anywhere.
He was arrested on May 14, 1971, four days after the last killing, and led police to the graves. He was convicted and sentenced to death, and hanged on January 22, 1976.
The case changed how Japanese police handled reports of missing young women in the 1970s, and it is also one of the most heavily written-up cases in modern Japan, in part because Okubo talked freely and at length about his method for the whole of his detention.