The discovery that prosecutors failed to reveal evidence that would have thrown serious doubt on the conviction of a Nepalese man for murder is likely to affect a court decision on whether to allow a retrial in the case, observers said.
The latest finding also may stir public debate over how evidence should be disclosed during trials.
It has been learned that the blood type of saliva detected on the breast of the victim during police investigations was different from that of Govinda Prasad Mainali. He was convicted and sentenced to life in prison for killing the woman, an employee of Tokyo Electric Power Co., in 1997.
The saliva indicates that the victim might have had contact with another man on the day of the crime. However, prosecutors did not disclose it during Mainali's trials.
"We had no choice but to believe prosecutors when they told us they'd presented everything [that could be reexamined]," said Hiroshi Kamiyama, chief lawyer for Mainali, at a press conference on July 26.
The lawyer made the remarks after he presented DNA test results as "new evidence that proves Mainali's innocence" to the Tokyo High Court, which is considering Mainali's request for a retrial.
The results of a new DNA examination of semen found in the woman's body revealed the possibility that another man was at her apartment the day she was killed. The DNA testing was conducted by prosecutors at the request of the high court on items that had been presented during Mainali's trials.
Prosecutors now have decided to conduct DNA testing on about 40 additional pieces of evidence, including the saliva. The high court will then rule whether such tests are applicable.
But defense lawyers likely will express strong objections over the fact that prosecutors failed to present many pieces of evidence, including the saliva testing results in question.
For many years, the Criminal Procedure Code did not stipulate in detail requirements for the disclosure of evidence. Consequently, prosecutors rarely disclosed evidence they felt unnecessary to establish someone's guilt.
However, there have been a number of cases in which convicted defendants turned out to be innocent after certain evidence was ultimately disclosed.
One such case was the 1949 Matsukawa Incident, which is said to be the largest case of false accusation--20 people were found guilty but later acquitted. There was also the 1967 Fukawa Incident, in which two men were acquitted in a retrial this June.
More specific provisions about disclosure of evidence were included in the Criminal Procedure Code in 2005, as part of steps taken toward the introduction of the lay judge system in 2009. Prosecutors are now required to disclose evidence that may support defense lawyers' arguments, not just evidence that supports their own, during pretrial procedures.
However, some observers say this is not enough to prevent prosecutors from concealing evidence.
"We must create a system under which all evidence is disclosed," said lawyer Keita Miyamura, a member of the Japan Federation of Bar Associations.