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A customs official said Tuesday night that Mr. Harris was not enrolled in any of the U.S. government’s trusted traveler programs, which could have allowed faster processing through security or customs. The official spoke on the condition of anonymity because he was not authorized to discuss details of the ongoing investigation.

Mr. Harris traveled from Kansai, in western Japan, to Incheon, Korea, before landing in Los Angeles.

An immigration officer at Kansai International Airport, Masahiro Nakamoto, said authorities did not report anything suspicious at the time Harris boarded. Spokesman Keisuke Hamatani said Kansai security officials had not reported any suitcases containing the hazardous materials U.S. authorities say they found in Mr. Harris‘ luggage.

Mr. Nakamoto said arriving passengers are checked more closely than those leaving the country.

Yasunori Oshima, an official at Japan’s Land and Transport Ministry’s aviation safety department, said there had been no official inquiry or request from U.S. authorities to look into the case, which he said would have been more of a concern if the hazardous materials were brought on board rather than checked.

“The case does not seem to pose any immediate concerns about aviation security measures in Japan,” he said.

Airport police said they do not believe the case constitutes illegal conduct under the Japanese domestic criminal code, but Japan may cooperate at the request of U.S. investigators.

Elliot Spagat reported from San Diego. Associated Press writers Rodrique Ngowi in Boston, Eric Talmadge and Mari Yamaguchi in Tokyo, and Alicia A. Caldwell in Washington contributed to this report.