Chinese media representatives swarmed around a small-statured man as he apologized before a memorial monument on the outskirts of the northeastern city of Harbin last August.

“I did something reckless and caused trouble to others,” Hideo Shimizu, 95, said.

The scene was repeatedly aired on Chinese news broadcasts and featured on the front pages of newspapers the following day under such headlines as: “Former Unit 731 member testifies to its crimes.”

But in Japan on social media, Shimizu’s apology immediately sparked outrage. Posters labeled him as “senile old man” and “elderly public nuisance.”

A resident of Miyata village in Nagano Prefecture, Shimizu has been subjected to such slander and abuse countless times over the past decade.

Unit 731 was the Imperial Japanese Army’s biological warfare unit established in the suburbs of Harbin in 1936.

It conducted human experiments, such as infecting Chinese and Russian prisoners of war with bacteria, resulting in numerous deaths.

Shimizu is one of the few surviving members of the unit. He served as a “child member,” a civilian attached to the military.

Before he graduated from the advanced course of a national elementary school in Nagano Prefecture, a teacher told him there was a job in Manchuria, the present-day northeastern China.

Without even knowing his destination, he arrived in Harbin in March 1945. He was 14 years old.

He was with Unit 731 for about six months until Japan’s surrender in World War II. But he is still haunted by a scene he witnessed in the headquarters building in July that year.

The shelves of the “specimen room” were lined with glass jars containing human internal organs, limbs and heads floating in formalin.

A superior officer told him that they were dissected from “maruta,” a covert term for the prisoners used as experimental subjects.

A pregnant woman was in a large jar, with a fetus with hair visible from her flayed side.

It was the first time Shimizu had seen a human corpse. He could not stop crying and had nightmares for several nights.

He kept silent about what he had seen and heard.

After the war, he obtained a license as an architect and was blessed with children and grandchildren. But he hid everything about his war past, even from his family.

The existence of Unit 731 was buried in history for some time.

However, Seiichi Morimura’s nonfiction work “Akuma no Hoshoku” (The Devil’s Gluttony) published in 1981 shed light on the clandestine unit.

Subsequently, U.S. military investigation records, which had been preserved in the United States, and Soviet documents on war crimes trials were discovered.

The U.S. military had interrogated senior members of the unit, including its leader, Shiro Ishii, immediately after the war.

A report dated Dec. 12, 1947, listed bacteria used in biological warfare research, such as botulinum, plague and typhoid, and referred to experimental data provided by senior unit members as well as “about 500 human specimens.”

Testimonies from former unit members accumulated, and the picture of vivisections and other atrocities committed emerged.

In a lawsuit on textbook screening over descriptions of Unit 731, the Supreme Court stated in 1997 that “the broad outline that (the unit) killed many Chinese and others through live human experiments has become an established academic consensus.”

Shimizu broke his silence in 2015, 70 years after the end of the war.

While out one day, he came across an exhibition on Unit 731 and confessed to his wife, who was beside him, that he had been a member of the unit. He began accepting invitations to give lectures and responding to media interviews.

He felt as if the burden on his heart was lifted a little by speaking of the memories he had long locked away.

At the same time, he learned that he was being attacked online.

A friend taught him how to use a computer, and he found such posts saying the “human experiments are fabricated.” Some messages were directed at him: “Old man, you are lying.”

Anger welled up inside him.

His name is listed on the roster of 3,607 unit members disclosed by the National Archives of Japan in 2018.

He had finally found the courage to share his memories after decades of nightmares, and he could not stand being called a liar so easily.

While acknowledging the existence of Unit 731, the government has neither confirmed nor denied its activities, such as human experimentation, citing lack of documentation.

In March, when the unit’s atrocities were raised in the Diet, Prime Minister Shigeru Ishiba said, “The means (to verify the facts) have been lost with history.”

The previous month, Shimizu gave a lecture at a school in Tokyo.

The slander that began last summer had subsided somewhat, but relatives told him not to “stir things up anymore.”

“If you say something did not happen 100 times, it becomes as if it really never did. That is frightening,” he said on his way home from the lecture.

“I am getting tired these days. This might be the last time,” he said, with his back hunched, as he boarded an express bus bound for Nagano.