The founder of Green Cross Corp., an Osaka-based pharmaceutical firm, played a major role shortly after World War II in preventing senior members of Unit 731 from being prosecuted as war criminals, it was learned Friday.

Ryoichi Naito, a physician and key member of the unit, drafted a plan in which unit leaders would hand over to the U.S. military most of the information related to the unit’s efforts to develop biological and chemical weapons.

However, Naito said information concerning their planned germ warfare and vivisection should never be disclosed, according to recent discoveries in the documents.

The documents, which are in the possession of Tsuneishi Keiichi, a professor at Kanagawa University, were confirmed to have been written by a senior member of Unit 731. General Headquarters claims it was unaware that the special unit was conducting research using prisoners of war from various countries, and gave the unit’s leaders immunity from prosecution.

Immunity was extended to the unit’s senior officials after two years of questioning by the U.S. military because the military put priority on obtaining the information on biological and chemical weapons.

Declassified documents at the Pentagon previously showed Naito as vowing to the U.S. Army in September 1945 that Unit 731 had never used humans as guinea pigs in experiments.

Most of the top-echelon leaders of the special force, officially called the 731st Epidemic Prevention and Water Supply Headquarters, avoided the gallows and continued in their medical careers after the war.

After the unit was disbanded following the war’s end in August 1945, Naito established the Japan Blood Bank, predecessor of Green Cross, in 1950. He died in July 1982. Green Cross, a leading supplier of blood products, is one of five drug firms named in lawsuits by hemophiliacs who contracted HIV through tainted blood products. Green Cross was ordered to pay damages in two suits, while others are ongoing.