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A 74-year-old Japanese citizen suspected of committing war crimes during World War II attempted to gain entry into the U.S. Thursday after taking a United Airlines flight from Tokyo to Chicago.

But federal authorities at O’Hare International Airport blocked Yoshiro Shinozuka, who had belonged to the infamous Unit 731 biological warfare group, from leaving customs and sent him back on the next flight to Tokyo.

“Because of his wartime activities, (Shinozuka) is not eligible to enter the United States,” said Immigration and Naturalization Service spokesman Bill Strassberger.

It was the first time since World War II that the U.S. government had barred a Japanese citizen from entering the country because the person was suspected of “crimes against humanity,” said a Justice Department spokesman.

Shinozuka and another former member of the Japanese Imperial Army had announced that they would try to enter the U.S. to talk about their role in Japan’s war crimes as part of a history exhibit touring five North American cities. No member of Unit 731, which reportedly dissected live POWs and civilians without anesthesia during experiments, has spoken publicly in the U.S. or Canada about Japan’s “forgotten holocaust.”

Asian scholars estimate that more than 15 million civilians died in China from torture and neglect during the 14-year Japanese occupation that began with the 1931 takeover of Manchuria.

Thursday’s action resulted from a 1996 decision by the Justice Department to add 16 suspected Japanese war criminals to a “watch list” of more than 60,000 Nazi war criminals.

“Anyone who participated in war crimes during World War II is inadmissible to the United States,” Strassberger said.

Accompanied by Japanese lawyers, Shinozuka arrived in Chicago at 9:39 a.m. on United Airlines Flight 884.

The Global Alliance for Preserving the History of World War II in Asia, a group based in Cupertino, Calif., had sponsored Shinozuka’s trip. The alliance-sponsored exhibit will stop in Toronto, New York, Washington, Vancouver and San Francisco.

Many Chinese-Americans want the U.S. government to allow Shinozuka and others to speak in the U.S. because they are among the few former Imperial Army members willing to talk openly about Japanese atrocities during World War II.

“This is a very good chance for the American government to investigate the whole thing,” said Jeff Chou, a Carol Stream business executive and chairman of a Chicago-based Taiwanese political group. “We should let (Shinozuka) speak and find out the truth.”