In Japan, the four-decade hunt for a notorious serial killer continues

In the photo on her "missing" poster, Yukari Yokoyama looks directly into the camera, a slight smile playing about her lips. The picture, more than two decades old, is one of the last that her parents took of their four-year-old daughter before she vanished in Ota, about 100km north of Tokyo, in July 1996.

Now, police in Gunma prefecture are making what is surely a final appeal for anyone to come forward who may have seen Yukari after she wandered off from her father in a pachinko parlour. The information they have may seem insignificant, the authorities say, but it could hold the key to the little girl's disappearance.

It could also help shed more light on the deaths of four girls over the previous 17 years, as it is believed that Yukari may have been the final victim of a serial killer who prowled a small area to the north of the capital. The bodies of the other girls were later discovered; only Yukari has yet to be found.

To emphasise that they are still treating this as a missing-person case and that they have not given up hope that she might still be alive, the police have added an artist's impression of what she might look like today, at the age of 28.

The reward of 6 million yen (US$56,000) is also prominently displayed on the posters and leaflets that are being handed out around Ota, but after all these years, experts are not optimistic that it will be enough to finally identify one of Japan's most notorious murderers.

The case is also infamous for police allegedly forcing a confession out of a man with learning disabilities who in 1991 was arrested and convicted of the fourth killing. He served 18 years in prison, only to be exonerated when a local journalist poked holes in the prosecutors' case.

"It will be, I fear, very difficult to identify the suspect in these killings now," said Shinichi Ishizuka, a professor of law and director of the criminology research centre of Kyoto's Ryukoku University.

"Too much time has gone by for people to remember where they were and what they were doing. There are too many questions about the investigation and the evidence."

The "missing" poster for Yukari Yokoyama includes an artist's impression of what she would look like now, at the age of 28. Photo: Handout

The first victim was Maya Fukushima, five, who went missing while playing at a shrine near her home in the town of Ashikaga " less than 10km from Ota " in August 1979. Her naked body was found in a backpack near the Watarase River six days later.

In November 1984, five-year-old Yumi Hasebe went missing from a pachinko parlour, only for her body to be discovered 16 months later in a field less than 2km from her home.

The killer next struck in September 1987, taking Tomoko Oosawa, eight, soon after she had left her home in Ota. Her body was found 14 months later by the Tone River.

Mami Matsuda, four, disappeared from another pachinko parlour in 1990 and was discovered dead the following day on the banks of the Watarase River.

The July 1996 abduction of Yukari Yokoyama bore a number of similarities with previous cases, including her disappearance from a pachinko parlour.

Inevitably, the apparent breakthrough in the 1990 killing of Matsuda caught the attention of the public and the media.

The following year, police formally arrested Toshikazu Sugaya, a local man who drove a school bus and was known to have learning disabilities, said Ishizuka from Ryukoku University, who later interviewed him.

Sugaya's conviction relied heavily on primitive DNA evidence and a confession. He also admitted to two of the other murders, but was never charged for them.

In 2007, local journalist Kiyoshi Shimizu began to look into the case more closely and determined that the DNA evidence used to convict Sugaya was ambiguous. He convinced the authorities to retest the sample with more modern techniques, which conclusively showed that Sugaya was not the murderer.

Other elements of the prosecution's case quickly fell apart. It was discovered that eyewitness reports that could have exonerated Sugaya had not been presented in court, and the timeline in his confession was impossible.

After 18 years in prison, Sugaya was released in May 2009 and subsequently claimed that he had only confessed after he was physically assaulted by Fumio Hashimoto, the detective who had headed the investigation. A retrial in 2010 found him innocent on all counts.

A pachinko parlour like the ones the victims were abducted from, pictured in Japan's Osaka in April. Photo: Kyodo

That same year, Shimizu reported that a new suspect had been identified, with DNA that matched Matsuda's killer and the discovery of security footage showing a man talking to young girls in shopping malls.

With the 25-year statute of limitations having expired on Matsuda's death, however, police have declined to make an arrest. Significantly, they have also refused to return a shirt that has the killer's semen on it to the family of the victim, which would permit additional independent tests to be carried out.

Shimizu, the journalist, has said that he believes the police made errors with the DNA tests or fabricated the results, but cannot admit it because the same tests were used to convict another man, Michitoshi Kuma, for the killing of two young girls in Iizuka City in 1992.

Kuma was 70 years old when he was hanged at the Fukuoka Detention Centre in October 2008, insisting to the end that he was innocent.

If the authorities were to admit they falsified or made a mistake with the DNA tests that incriminated Sugaya, the conviction and execution of Kuma would also be called into question.

"There are serious problems with the DNA from Sugaya's conviction, on top of the forced confession, and this case is one of the reasons why all police interrogations are now recorded," said Ishizuka, the Ryukoku University law professor.

"I think that standards are higher now. DNA evidence is important in a case and police can no longer simply rely on a confession. Society now demands that there has to be absolute proof."

Still, the girls' killer remains at large.

The leaflets that are being handed out in Ota also have three other blurry black-and-white images captured from security cameras in the pachinko parlour where Yukari Yokoyama was last seen. They are of a man wearing dark, baggy trousers with a white T-shirt under a black jacket, sunglasses and a peaked cap.

He is smoking in one of the images, and is estimated to be 158cm tall; in another, he is seen talking to Yokoyama. His identity remains a mystery.

This article originally appeared on the South China Morning Post (SCMP).

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