The Nagoya high court is set to declare whether 86-year-old Masaru Okunishi should face a retrial over the killings half a century ago, a court spokesman said Thursday.
Okunishi, who has spent much of the last four decades in solitary confinement, has consistently protested his innocence after retracting what he says was a coerced confession ahead of his original trial.
Five women died and 12 others fell ill after drinking wine laced with agrichemicals at a community get-together in the small town of Nabari, central Japan in 1961.
Okunishi initially told police that he put the lethal chemicals into white wine in an attempt to kill both his wife and his mistress and erase their complicated love triangle.
But he later withdrew his confession and was acquitted. A higher court overturned that acquittal and sentenced him to death, a sentence confirmed in 1972 by the Supreme Court.
Since then, he has become one of Japan’s longest serving death row inmates, despite repeated attempts by his lawyers to get a retrial on the basis that the women all died from consuming different chemicals.
“I have a big hope and expectation of a (positive) decision,” Okunishi said in a message sent to local media through his supporters.
Under Japanese law death row inmates can be retried if judges rule new evidence can legitimately reverse the verdicts.
Apart from the United States, Japan is the only major industrialised democracy to carry out capital punishment, a practice that has led to repeated protests from European governments and human rights groups.
International advocacy groups say the system is cruel because death row inmates can wait for their executions for many years in solitary confinement and are only told of their impending death a few hours ahead of time.