I once had a conversation with a retired judge in Japan. He said that although there seems to be a strong belief that the DNA testing is a new golden solution, he thinks we still need to be careful. He suggested that the fact that there was a “match” of DNA evidence found at the crime scene (or from the body of the victim etc.) alone should be used to exonerate someone, but not to implicate someone.
Yes, there is always a possibility that the state-of-the-art DNA testing result is faulty: there might have been a contamination of the materials or the testing might not have been conducted properly, and there have definitely been mistakes made in the past that were revealed later.
Indeed, there is a very well known case in Japan (Ashikaga Case) where a man was implicated by faulty DNA evidence and later exonerated by more sophisticated DNA evidence.
In May of 1990, the body of a 4-year-old girl was found dead near the Watarase River in Ashikaga City. The clothing of the victim was found from the river. The clothing had the perpetrator’s semen on.
Many became suspects until in November 1990 the police began to suspect Toshikazu Sugaya, who was a school bus driver. They followed Sugaya for nearly a year.
In June 1991, they obtained some Kleenex that had his semen on from the garbage he threw out. They sent the Kleenex together with the victim’s clothing to the police crime lab to conduct a DNA testing.
The result came back in November 1991. The crime lab extracted DNAs and amplified the MCT 118 loci with a PCR amplification kit. They determined the MCT 118 type using 123 bp Ladder. By then, the MCT 118 method was only in use for one year in the police department. The first DNA testing was done in 1989. This was one of the first cases the police used DNA analysis. The lab concluded that there was a match and the DNA type was predicted to have the frequency of 1.2 in 1,000.
With this result, the police interrogated Sugaya voluntarily on December 3, 1991. Sugaya eventually confessed to the crime, after the police told him that there was a DNA match. He later recanted the confession, but the prosecutors interrogated him during trial, and because of the pressure, he confessed the crime again in front of judges (which he later recanted again). The main evidence against Sugaya was his confessions (made both during trial and investigation) and the DNA evidence.
Some circumstance of the crime clearly did not match Sugaya‘s confession. Although Sugaya stated in his confession that he suffocated the victim using both hands, the marks in victim’s neck suggested that the perpetrator suffocated her using only the right hand. In addition, the autopsy suggested that she drowned, not suffocated to death.
The court nevertheless found him guilty and sentenced him to life imprisonment.
The High Court as well as the Supreme Court affirmed the decision. In fact, the 2000 Supreme Court decision in this case was long cited after and was a leading decision on the admissibility of DNA evidence. It was the first Supreme Court decision ever to rule on the matter.
After the decision became finalized, Sugaya went to serve his sentence in prison.
In 2002, Sugaya, with his lawyers, filed a petition for retrial in the District Court. The District Court denied his petition, so Sugaya appealed to the High Court. The High Court in 2008 finally decided to commission a retesting on the clothing of the victim. They did a PCR, mitochondrial as well as another more accurate MCT 118 type DNA testing.
The results came back in 2009, and it was concluded that the DNA that was on the clothing of the victim was not Sugaya’s.
Sugaya was released in 2009 after 17 and a half years of incarceration, and the High Court decided to grant his petition for retrial. He was finally declared innocent by the District Court in 2010. During his retrial, prosecutors finally admitted that the police forced Sugaya to confess using force in the initial interrogation.
Sugaya got a compensation in 2011 from the Japanese government. He was awarded about 1 million dollars for the 17 and half years he had to spend in prison for the crime he did not commit.
Read a detailed report on the Ashikaga case by the Japan Bar Association here (in Japanese).