Japanese court acquits longest-serving death row prisoner

Hideko Hakamada, sister of Iwao Hakamada leaves the Shizuoka District Court in Shizuoka. [Philip Fong, AFP]

The world's longest-serving death row prisoner was acquitted on Thursday, more than half a century after his murder conviction, when a Japanese court ruled that evidence had been fabricated.

Ailing health prevented 88-year-old former boxer Iwao Hakamada from being in the court to learn the outcome of his retrial, which was granted a decade ago after a long campaign by supporters.

But his 91-year-old sister Hideko, who often speaks for him, bowed deeply to the judge who declared Hakamada innocent.

"Everyone -- we won the acquittal, it's all thanks to your support," she said outside the Shizuoka District Court, close to tears with her voice cracking.

Hakamada spent 46 years on death row after being convicted in 1968 of robbing and killing his boss, the man's wife and their two teenage children.

"Investigators tampered with clothes by getting blood on them" which they then hid in a tank of miso, or fermented soybean paste, said Thursday's ruling, seen by AFP.

It slammed the use of "inhumane interrogations meant to force a statement... by imposing mental and physical pain".

"The prosecution's records were obtained by effectively infringing on the defendant's right to remain silent, under circumstances extremely likely to elicit a false confession," the ruling said.

Hundreds of people queued in the morning to try to secure a seat for the verdict in a murder saga that has gripped the nation and sparked scrutiny of Japan's justice system.

Prosecutors have two weeks to appeal, according to Japanese media.

Hideko told a post-trial news conference that the not guilty verdict had "sounded divine".

She wore a white jacket and, asked before the verdict if it symbolised her brother's innocence, said she had deliberately avoided dark colours.