A man convicted in a 1966 quadruple murder case filed an appeal Monday with the Supreme Court to seek a retrial, even though he was freed in 2014 after spending nearly half a century on death row, his lawyers said.

Former professional boxer Iwao Hakamada, 82, has been struggling to clear his name over the murder in Shizuoka Prefecture he had initially confessed to, but the Tokyo High Court on June 11 scrapped a decision by the Shizuoka District Court to grant him a retrial.

Court judgements have been divided over the credibility of DNA tests on five items of clothing said to have been worn by the culprit. The district court concluded that the items were unlikely to be Hakamada's based on an expert analysis provided by his defense team, whereas the high court said the analysis was unreliable.

Hakamada was freed by the district court in March 2014 after nearly 48 years in prison. The court, in addition to ordering the reopening of the case, suspended his death sentence as well as his continued detention.

Hakamada, who now lives in Shizuoka Prefecture with his older sister, has not been placed back in detention so far, with the high court saying that given his age and health condition, he is unlikely to flee.

The former boxer continues to be haunted by fears of death and is suffering from delusions apparently as a result of his long detention, according to people close to the matter.

(Iwao Hakamada at his home in Shizuoka Prefecture, central Japan)

Hakamada was a live-in employee at a soybean processing firm when he was arrested in August 1966 for the murder of the firm's senior managing director, his wife and two children. They were found dead from stab wounds at their burned house in Shizuoka Prefecture.

Hakamada initially confessed to investigators before changing his plea at trial. But the district court found Hakamada guilty and sentenced him to death in 1968, with the decision finalized by the Supreme Court in 1980.

As Hakamada and his family sought retrials, a new development was seen in 2014 when the district court accepted DNA test results that undermined the claim that Hakamada's blood had been detected on five items of clothing found in a soybean tank in the processing plant. The court even noted that the evidence could have been fabricated by police.

Prosecutors appealed against the decision to the Tokyo High Court, casting doubt on the reliability of the DNA tests, and the high court pointed to "serious doubt" regarding the methodology of the DNA tests.