Longest-serving death row prisoner hails acquittal 'victory'

The world's longest-serving death row prisoner thanked his supporters for helping him achieve "complete victory" after a Japanese court last week overturned his decades-old murder conviction.

After a long fight for justice led by his sister, 88-year-old Iwao Hakamada was on Thursday declared innocent of the quadruple murder that he spent 46 years on death row for.

"Finally I have won full and complete victory," the former boxer told a group of supporters on Sunday in Shizuoka, the region southwest of Tokyo where the ruling was issued.

"I couldn't wait any longer" to hear the not-guilty verdict, said a smiling Hakamada, sporting a green hat.

"Thank you very much," he added, accompanied by his 91-year-old sister Hideko at the meeting, which was shown on Japanese television.

Japan and the United States are the only major industrialised democracies to retain capital punishment, which has broad support among the Japanese public.

Hakamada is the fifth death row inmate granted a retrial in Japan's post-war history. All four previous cases also resulted in exonerations.

Decades of detention -- mostly in solitary confinement with the threat of execution constantly looming over him -- have taken a toll on Hakamada's mental health.

His lawyer and supporters have described him as "living in a world of fantasy".

Hakamada was released in 2014 pending the retrial but rarely speaks publicly.

Despite the retrial verdict, his acquittal isn't finalised -- prosecutors reportedly have until October 10 to decide whether to appeal the Shizuoka District Court's ruling.

But they may face an uphill battle, as the court delivered a sweeping rebuke of the prosecution's arguments, saying that investigators fabricated key pieces of evidence.

Hakamada's initial confessions of having robbed and murdered his boss, the man's wife and their two teenage children were obtained through "inhumane" interrogations and mental and physical torture, making them invalid, the ruling said.

Blood-stained clothes used to incriminate him were also ruled a set-up. The court said investigators had put blood on them and planted them in a tank of miso fermented soybean paste to be discovered.

Once last week's verdict is finalised, it would pave the way for Hakamada to be compensated to the tune of more than 200 million yen ($1.4 million) under the law, according to one estimate by lawyers.

On top of that, the defence team is considering launching a new lawsuit against the state seeking further compensation, Hakamada's lead lawyer Hideyo Ogawa told a news conference on Monday.

Given the ruling went so far as to condemn a "concerted" effort by prosecutors and police to make up evidence, "I believe it gave us a sufficient basis to sue the state", Ogawa said.

His client was absent from the news conference because of poor health.

Hideko, who did attend, recounted the moment when she broke the news of the acquittal to her brother as he was "relaxing after his bath time".

"But he was all silent... I think part of him is still in doubt that this really happened," she said.

When asked about the possibility that prosecutors might opt to pursue the case, a confident Hideko replied, "if they want to, then go ahead and suit yourself".