Unit 731 was the creation of a brutal psychopath, Lieutenant-General Ishii Shiro. His perverted imagination was captured by the possibilities of biological and chemical warfare, and in the Japan of the 1920s and '30s, he found supporters in the increasingly nationalistic and fanatical military.

Part of his fame came from the invention of a water filter that would be used by the Japanese military in the field. Yet even this innocuous invention had a connection with the grossness of Ishii's character. He once reportedly demonstrated the effectiveness of the filter to Emperor Hirohito by urinating through it, and offering the result to the Hirohito to drink. The Emperor declined, so Ishii drank it himself.

Water purification was also to have a link with the grisly activities of Unit 731. The official cover name for the unit was the Water Purification Bureau.

This latest court case, which began in 1997, has revealed much about the operations of the unit. One of the most harrowing testimonies has come from a former member of the unit, Yoshio Shinozuka, who has declared his remorse, and has vowed to tell the truth about the atrocities committed in China.

Shinozuka revealed in horrific detail what occurred at the unit headquarters in Ping Fang, just outside Harbin in northern China. The Chinese victims were known as "logs", and it was Shinozuka's job to scrub them down before the vivisection.

"I still remember clearly the first live autopsy I participated in," he recalled. "I knew the Chinese individual we dissected alive because I had taken his blood once before for testing. At the vivisection, I could not meet his eyes because of the hate he had in his glare at me."

The victim had been infected with the plague, and was totally black. Shinozuka was reluctant to use the brush on the man's face. "Watching me, the chief pathologist, with scalpel in hand, impatiently signalled me to hurry up," he recalled. "I closed my eyes and forced myself to scrub the man's face with the deck brush. The chief pathologist listened to the man's heartbeat with his stethoscope and then the procedure started."

The case before the Tokyo court also heard from the victims, and family of the victims, in villages and towns infected by the plague and cholera between 1940 and 1942.

Peize Xue was a young boy in Jiangshan when the Japanese infected the area with cholera. He recalled how his sister's three children had been struck down: "The three little ones died such tragic deaths. They were poisoned by the Japanese army," she sobbed. "Before Shuanglan (aged eight) passed away, she asked me, lying limply on her bed, to build a small casket for her."Sixty years on, these testimonies have a powerful and revelatory impact, in part because the activities of Unit 731 and related units remained forgotten until relatively recently. It was only in 1981 that international attention refocused on these awful events when an American journalist, John W. Powell junior, published A Hidden Chapter in History, alleging an American cover-up. Since then, academics and journalists have built an impressive case that details how Ishii and other key players received immunity from prosecution in return for supplying their research to American scientists.

In a secret diary, Peaty recorded the regular injections of infectious diseases, disguised as harmless vaccinations, which were given to them by doctors visiting from Unit 731. His entry for January 30, 1943, records: "Everyone received a 5cc typhoid-paratyphoid A inoculation." On February 23, his entry read: "Funeral service for 142 dead. 186 have died in 5 days, all Americans." Further "inoculations" followed.

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