It was a moment that Iwao Hakamada had long been waiting for. But at 84 years old and with psychological problems developed during decades on death row, he could not grasp its significance.

His sister, Hideko, 87, showed him a letter from the Supreme Court about a decision that could lead to his acquittal of a conviction for a 1966 multiple murder that he has insisted he did not commit.

The Supreme Court on Dec. 22 overturned a lower court ruling and sent the case back to the Tokyo High Court, giving Hakamada a chance to clear his name in a retrial.

Hakamada, however, told her sister, “The retrial has already ended.”

Hideko acknowledged that she would be 88 next year and her brother 85, but she said she was confident that she would live to see the day her younger brother is cleared of the murder conviction made close to 50 years ago.

“We will continue to do our best” to seek an acquittal, she said.

Hakamada and his lawyers were seeking a retrial for his conviction of stabbing four members of a family to death during a robbery and setting fire to their home in Shizuoka Prefecture in 1966.

The family operated a miso business that employed Hakamada, a former professional boxer.

Hakamada was sentenced to death in 1968. He suffered from psychological problems while on death row, knowing that he could be executed on any given day.

The Shizuoka District Court in March 2014 called for a retrial in the case and granted his release.

But the Tokyo High Court in June 2018 overruled that decision and denied Hakamada a retrial.

The dispute was sent to the Supreme Court.

The court’s Third Petty Bench outlined a number of points that the Tokyo High Court should look into, including five pieces of clothing found in a miso tank at the company where Hakamada had worked.

The clothing was found in August 1967, about a year after Hakamada was arrested.

Prosecutors said blood stains on the clothing were reddish when the evidence was found.

Supporters of Hakamada conducted experiments on blood-stained clothing by curing the items in miso for long periods.

The Supreme Court ruling noted that in those experiments, the blood turned blackish about a month after being cured in miso, and that no red blood stains remained. It added that a similar experiment conducted by prosecutors also found no red stains after about five months.

Based on the experiments, defense lawyers said the period before the clothing was found was shorter than the original 14 months or so since the murders. They argued that the lack of red blood stains on the clothing meant that someone other than Hakamada had discarded the clothing in the miso tank after his arrest.

The defense team said the blackening of the blood was the result of a Maillard chemical reaction caused by the mixing of the proteins in the blood with the sugars in the miso.

The Supreme Court faulted the Tokyo High Court for not turning to expert knowledge to look more deeply into the extent of the Maillard reaction. It ordered the high court to concentrate on that aspect to determine if there was any reasonable doubt that Hakamada committed the crime.

(This article was compiled from reports by Shunsuke Abe, Takashi Uematsu and Kazutaka Toda.)