Prosecutors have apologized for concealing critical evidence that might have cleared Iwao Hakamada, the former professional boxer who spent more than 40 years on death row before being released from prison in March, according to his lawyers.

The head of Hakamada's legal team, Katsuhiko Nishijima, alleged at a news conference on Tuesday that prosecutors had admitted making incorrect claims, concealing the existence of photographic negatives showing bloodstained clothes said to have been worn by the culprit.

Hakamada, 78, was a live-in employee at a soybean processing company when he was arrested in August 1966 on robbery, murder and arson charges. The Shizuoka District Court sentenced him to death in 1968 for allegedly slaying an executive of the company, his wife and their two children in Shizuoka Prefecture.