Japan has again been forced to confront its wartime conduct after a former doctor in the country's imperial navy admitted he had conducted experiments on Filipino prisoners during the second world war.
Akira Makino, 84, said in an interview with the Kyodo news agency that he had performed surgery and amputations on dozens of prisoners of war before they were executed in the Philippines.
Several veterans have admitted conducting human vivisection in northern China as part of Japan's wartime chemical and biological weapons programme, but experts say Mr Makino is the first to testify that similar atrocities took place in south-east Asia.
Mr Makino said that as a 22-year-old he had operated on about 30 prisoners between December 1944 and February 1945 while working as a medic on the island of Mindanao.
As part of his medical training he said he had been ordered to conduct amputations, abdominal dissections and other experiments on condemned men, women and children, including two men who had been beaten unconscious for allegedly spying for the US.
After sedating the men by placing ether-soaked cloths over their faces, he was instructed to make an incision with a surgical knife and study their livers.
"I thought, 'What a horrible thing I am doing to innocent people, even though I had been ordered to do it,'" he told Kyodo.
Mr Makino said he was too scared to refuse. "I would have been killed if I had disobeyed the order," he said. "That's how it was in those days."
Filipino patients who survived their ordeal were strangled with rope.
Mr Makino is one of several former Japanese soldiers who decided to reveal the truth about their country's use of human guinea pigs before they die.
Unit 731, the imperial Japanese army's notorious germ warfare unit, killed thousands of Chinese civilians and Allied PoWs at its sprawling complex in Harbin, northern China, from the late 1930s until the end of the war.
The victims, named "logs" by their torturers, were injected with typhus, cholera and other diseases. They died during the experiments or were executed to prevent them from talking about their experiences.
As the end of the war approached, the unit destroyed evidence of their activities, releasing infected animals and dumping chemicals into rivers. The extent of their activities only came to light following testimony from repentant former doctors, soldiers and nurses.
Hal Gold, author of Unit 731:Testimony, said Mr Makino was typical of medical students and young doctors who were sent overseas by their superiors. "A lot of those guys didn't have a choice," said.
"They had to follow orders, so it's hard to pass a moral judgment on people like that. As you go further down the line of command, many of them didn't know what they were getting into. If they refused orders, it was the end of their medical careers."
With many surviving former members of the unit now in their 80s and 90s, he said Mr Makino may be among the last to talk frankly about their work.
"There's a pretty slim prospect of anyone in authority coming forward," he said. "Our only hope is that someone discovers a letter or a diary, something that may have been hidden by the family because they were ashamed."
The US authorities secretly granted unit officials immunity from prosecution in return for access to years of research into biological weapons. Several former Unit 731 officials went on to enjoy prominent careers in medicine, academia and business, including its former leader, Dr Masaji Kitano, who headed Green Cross, once Japan's biggest pharmaceutical company.
Mr Makino, who lives near Osaka, said he remained haunted by memories of the experiments and had ignored friends who urged him to take his secret to the grave. "We should not repeat that misery again," he said. "I want to tell the truth about the war."