Ogata was born on February 25, 1962 in Fukuoka prefecture. She met Matsunaga in the 1980s and lived with him while he ran a fraudulent futon business. Over years he isolated her from everyone else, beat her, controlled what she ate and where she went, and used her to reach her own family.
Between 1996 and 1998 seven people died in a flat in Kitakyushu: Kumio Toraya, thirty-four, a former employee, and his daughter, and five members of Ogata's family: her father Takashige, sixty-one, her mother Shizumi, fifty-eight, her sister Rieko, thirty-three, her brother-in-law Kazuya, thirty-eight, and the children Yuki, five, and Aya. They were starved, beaten and shocked with a device wired to the mains. Matsunaga directed members of the family to kill one another and to dismember and dispose of the bodies, and Ogata took part in the killings and the disposals.
The case emerged in March 2002 when her ten-year-old niece escaped and reached her grandparents. Both were arrested on March 6, 2002. No human remains and no physical evidence of any of the seven deaths were ever recovered; the prosecution rested on Ogata's testimony, the surviving child's, and Matsunaga's statements.
She was sentenced to death on September 28, 2005. On September 26, 2007 the Fukuoka High Court reduced the sentence to life imprisonment, holding that she had been under Matsunaga's psychological domination to a degree that substantially reduced her culpability. That finding rested on years of documented abuse and on her having been the principal witness against him. Matsunaga's own death sentence was confirmed the same day.
Whether the reduction was right is argued in Japan to this day, and the argument matters beyond the case: she participated in the deaths of her own parents, sister and nephew, and the court's answer was that the man who orchestrated it bore the responsibility. The count of seven is the same seven as in Matsunaga's entry, not an additional set.