Killing of Yasuko Watanabe

Yasuko Watanabe was a 39-year-old Japanese woman who worked as a senior economic researcher at the Tokyo Electric Power Company (TEPCO) in Tokyo. On 9 March 1997 she was strangled in the Shibuya area of Tokyo, and her body was found on 19 March 1997 in a vacant apartment in the Maruyamacho neighbourhood of Shibuya. Watanabe was also reported to have engaged in sex work in the evenings, and investigators recovered a personal journal in which she had recorded client encounters. The killing drew sustained national attention and heavy press coverage.

Suspicion fell on Govinda Prasad Mainali, a Nepalese man who lived in a nearby apartment in the same building and who had overstayed his visa. He was detained in March 1997 for the immigration violation and was later charged with the murder. Mainali acknowledged having paid Watanabe for sex on earlier occasions but denied any involvement in her death, and no eyewitnesses placed him with her at the time of the killing.

The court proceedings produced conflicting outcomes. In April 2000 the Tokyo District Court acquitted Mainali of murder, citing insufficient evidence. Prosecutors appealed, and on 22 December 2000 the Tokyo High Court reversed the acquittal, found him guilty, and imposed an indefinite prison sentence. Mainali remained imprisoned for roughly fifteen years.

The case ultimately turned on forensic evidence that emerged years later. In July 2011, DNA testing was carried out on semen recovered from the victim, material the prosecution had earlier described as too limited to analyse. The results excluded Mainali as the source and were consistent with an unidentified man, matching other biological evidence from the scene, including hair, a bloodstain on the victim's coat, and saliva. Some of this evidence had not been disclosed to the defence until 2011.

On the basis of the new findings, the Tokyo High Court set aside Mainali's conviction and ordered a retrial in June 2012. He was released, but immigration authorities deported him to Nepal for his earlier visa violation, and he returned to Kathmandu that month. In November 2012 the Tokyo High Court formally acquitted him, upholding the original 2000 district court ruling, and prosecutors did not appeal. In 2013 he was awarded compensation for his wrongful imprisonment.

The reversal was widely described as a serious miscarriage of justice, prompting criticism of practices such as prolonged pre-trial detention, prosecutorial appeals of acquittals, and non-disclosure of exculpatory evidence. The identity of the man whose DNA was recovered from the scene has not been publicly established, and no other person has been convicted of Watanabe's killing.