Hideo Shimizu, a former member of Unit 731, the notorious Japanese germ-warfare detachment during World War II, testified and apologized on Tuesday for the crimes committed by the unit during the Japanese invasion of China during the war.

Shimizu arrived by plane in Harbin, Northeast China's Heilongjiang Province, on Monday evening and visited the Exhibition Hall of Evidence of Crimes Committed by Unit 731 of the Japanese Imperial Army on Tuesday, according to media reports. 

Shimizu, 94, was among the last batch of Unit 731 Youth Corps members sent by Japan to Harbin, China, where he spent more than four months witnessing the war crimes committed by the unit, including the cultivation of pathogens, human dissections and human experiments, according to Xinhua. He fled China with retreating Japanese forces on August 14, 1945.

"The war ended 79 years ago, and most members of Unit 731 have passed away. Shimizu is the sole  surviving member who is willing to expose the Unit's crimes publicly, and he is likely to be the last Unit 731 member to return to Harbin," said Jin Chengmin, curator of the exhibition hall, as reported by Xinhua.

In 2016, Shimizu revealed his identity as a former Unit 731 member and began to expose the atrocities of the Japanese Imperial Army through public speeches and interviews, aiming to tell historical truths.

Unit 731 was a top-secret biological and chemical warfare research base established in Harbin as the nerve center for Japanese biological warfare in China and Southeast Asia during World War II.

At least 3,000 victims were used in human experiments by Unit 731, while more than 300,000 people in China were killed by Japan's biological weapons, Xinhua reported.