RESEARCH by a mainland professor has unearthed first-hand evidence of the Rape of Nanjing, in which thousands of Chinese were massacred by the invading Japanese army in 1937. Zhang Kaiyuan, a history professor at Central China Normal University, who accidentally found the wartime documents at Yale University in the United States three years ago, has recently completed his studies on the massacre. He said the documents showed the Japanese army had turned the eastern China city into a killing field. The evidence was contained in 132 boxes of letters, documents and photographs taken in China during World War II. It is believed to be the largest library of documents available on the atrocity. Among them are 17 bundles of letters describing the brutality of the Japanese army and photographs of Chinese comfort women. 'A few Japanese historians and nationalists argued that there was insufficient first-hand material recording what had actually happened during that period,' Professor Zhang said. 'They denounced the atrocity as a myth invented by the United States-dominated international war crimes tribunal to inflate Japan's past military aggression.' 'The archives will be the best evidence found to prove the Japanese military's wrong-doing,' Professor Zhang added. The material belonged to the International Relief Committee of Nanjing, an aid-relief organisation set up by 28 expatriates in China during the war. Professor Zhang said that the documents had strong credibility because they were mainly written by American missionaries who were in China before the US declared war on the Japanese. The chairman of the aid-relief group was a German who belonged to the Nazi Party, the professor added. The letters contained detailed accounts on the war crimes carried out by the Imperial Japanese army in Nanjing, including killings and rapes. One of the letters said 8,000 rapes took place in Jianing University, with the victims including children and old women. Professor Zhang said that the documents were smuggled out of China and were used by a journalist on the British newspaper, Manchester Guardian, in his reporting on the massacre a year after it occurred.